Patent Publication Number: US-2003232682-A1

Title: Automatic variable ratio differential

Description:
TECHNICAL FIELD  
       [0001] This invention represents an advance in the field of vehicle differentials which transmit driving torque from the engine to the driving wheels. It allows the driving wheels to rotate at different speeds when the vehicle is in a turn so that the wheels each travel the proper distance, and automatically senses and adjusts the torque sent to each driving wheel.  
       BACKGROUND ART  
       [0002] This invention generally relates to the use of a group of torque-sensing and speed-sensing differential devices in combination to produce a true mechanical ratio for proportioning torque between the driving wheels of a vehicle. Although the present invention is in no sense limited to use with the axles of motor vehicles, the herein illustrated forms which the invention may take are particularly adapted for use in motor vehicles. For this reason, the objects and advantages hereinafter disclosed will have specific reference to motor vehicles, but such objects and advantages are intended to extend to other types of construction wherein any one of the desired characteristics of the automatic variable ratio differential would be advantageous.  
       [0003] The purpose of a differential in motor vehicles is to transmit power to the driving wheels while allowing the driving wheels to spin at different speeds. Originally in the development of motor vehicles, the driving wheels were connected to a single, solid axle. This design, however, proved flawed because, although it did transmit the power effectively to the drive wheels, it forced the drive wheels to spin at the same speed. This is precisely the desired result when the vehicle is traveling in a straight forward direction. Unfortunately, a solid axle causes problems when the vehicle turns. In a turn, the inside wheels (those on the side towards which the vehicle is turning) do not travel as far as the outside wheels; this is simply a function of the arcs that the different wheels must travel. If the wheels are joined by a single, solid axle, then there must be scuffing and dragging on the wheels to account for this difference in the distances that they must travel. This wears the tires of the vehicle, produces stress in the axle, and results in a less comfortable ride for the passengers inside the vehicle.  
       [0004] An open differential is the conventional way to overcome this problem. This means that there are two independent axles (one for each drive wheel) connected together by a system of gears known as an open differential. The purpose of the open differential is to allow the two driving axles to rotate at different speeds while still receiving power from the engine. The result of the open differential is a much better ride: when the vehicle is traveling straight forward, the open differential acts as if it were locked, and the two axles rotate as one, but when the vehicle turns, the open differential allows the two axles to spin at different speeds (with the outside axle spinning faster than the inside axle) so that the wheels each travel the correct distance.  
       [0005] Unfortunately, the open differential has problems of its own. Because of the manner in which it allows the two axles to spin at different speeds, the open differential can sometimes result in the vehicle becoming stuck. The open differential always sends equal torque to each of the driving wheels. The amount of torque that it can send is limited based on the minimum tractive force available at the wheels. Thus, when one of the wheels slips (such as when a wheel is on ice or in mud) and there is not much tractive force, the vehicle can not move forwards even if the other wheel has very good traction because the open differential will not transmit enough torque. In such instances, a vehicle without an open differential (a single, solid axle) would not be stuck because the torque transmitted to the driving wheel with traction would not be limited by the lack of traction under the other wheel. But, in vehicles with an open differential, the wheel without traction would spin very quickly as it slipped while the wheel with traction would sit motionless as it does not receive enough torque to move the vehicle forward.  
       [0006] There are devices available to help deal with this functional flaw in an open differential. The simplest way to overcome this problem is to employ a locking mechanism that will link the two independent axles together so that they function as a single, solid drive axle. In effect, this device allows the driver to turn off the open differential in situations where it will function to prevent forward motion. Such a device, however, is cumbersome in size and weight and is slow in action, usually requiring the vehicle to be stopped before the locking can occur. Another attempt to solve the slipping-wheel problem in an open differential is a limited-slip differential. This device in essence is an open differential with a friction device that provides resistance to an axle that is slipping in order to simulate tractive force on the slipping wheel or a differential designed using inefficient gears so that the device always transmits some torque to a wheel with traction. The problem with these limited-slip devices is that they are inefficient and they wear out fairly quickly.  
       [0007] The Automatic Variable Ratio Differential (AVRD) solves the slipping-wheel problem in a more efficient way. It uses an open differential in conjunction with either fixed differentials or planetary gear sets. The result is that the AVRD allows the two drive axles to rotate at different speeds so that it performs the function of a standard open differential when the vehicle is in motion (the axles act as one when the vehicle goes straight but, when the vehicle turns, the outside axle spins faster than the inside axle) but it also prevents the vehicle from being stuck when one wheel is slipping by channeling torque to the wheel with traction. The AVRD accomplishes this by sending the wheel with traction a multiple of the torque that the slipping wheel can handle (based on the tractive force). If the slipping wheel has absolutely no tractive force, then the wheel with traction will not get any torque (since a multiple of zero is still zero), but if there is any tractive force at all (and there always is in the real world even if the coefficient of friction is low), then the wheel with traction will receive much more torque than that available to the slipping wheel. The AVRD channels torque based upon the conditions it senses from the ground-link. Thus, the AVRD channels the available driving power to the location where it is most effective by using a true mechanical ratio.  
       [0008] In some configurations, the AVRD also has the added benefit of providing a tighter turning radius. This improved maneuverability results from the ability of some AVRD configurations to create an inside reverse. Thus, the inner wheel in a turn will rotate backwards as the outer wheel continues to rotate forwards. The result is a force couple acting on the vehicle, and this allows the vehicle to turn rapidly.  
       DISCLOSURE OF INVENTION  
       [0009] The AVRD uses a standard open differential in conjunction with either fixed differentials or planetary gear sets to achieve its objectives. There are several different types of standard open differentials, including spur gear types, bevel gear types, and planetary types and also including limited slip differentials, but they all act similarly to produce identical results. A standard open differential gear system divides the torque of a rotational prime mover between the two axle shafts of a vehicle and allows them to rotate at different speeds when turning corners. There are several different configurations, but they generally involve the use of a ring gear, some planet gears, a differential carrier, and two output gears which connect to shafts. Basically, the prime mover provides the input to the differential through the drive shaft pinion. The ring gear (or other rotary input device), which also acts as the differential carrier of the open differential, is driven by the drive shaft pinion. Thus, the differential carrier, which generally houses the open differential gears, rotates at the speed of the ring gear. The planet gears are mounted on stub-shafts fixed to the differential carrier and orbit the output shaft axis at the same speed as the ring gear. When used in the ordinary manner, the output side gears of the differential are connected to the driving axles, which are subsequently connected to the drive wheels of the vehicle. Thus, when the vehicle is traveling in a straight line, the two output side gears (and thus the two axles) revolve at the same speed and there is no relative motion between the planet gears and the two output gears. The planet gears do not rotate on their stub shafts, serving only to transmit motion from the planet carrier to both wheels.  
       [0010] When the vehicle is making a turn, the inside wheel makes fewer revolutions than the outside wheel because of its shorter turning radius. If this difference in speed between the two wheels were not compensated for in some way, one or both of the wheels would have to slide to make the turn. The differential allows the wheels to rotate at different rotational speeds while at the same time delivering power to both. While in a turn, the planet gears rotate on their stub-shafts and permit the output side gears (and thus the axles) to revolve at different speeds relative to one another.  
       [0011] It can easily be seen that if one output shaft is stopped, the other will rotate at twice the speed of the ring gear; this is because the differential carrier (which is attached to the ring gear) rotates at the average speed of the two output shafts. The differential&#39;s purpose is to differentiate between the speeds of the two wheels. In the usual automobile differential, the torque is divided equally no matter whether the car is moving in a straight line or not. Often road conditions are such that the tractive effort that can be developed by the two wheels is unequal. When this happens, the total tractive effort available will be only twice that of the wheel having the least traction, because the differential divides the torque equally. Should one wheel be resting on snow or ice, the total effort available is very small and only a small amount of torque will cause the wheel to spin. In a standard open differential, the planet pinions serve as balance levers between output gears. The teeth have an involute profile; the normals to the profiles at all points of contact pass through the pitch points, so the lever arms always remain equal: thus the differential is always in balance.  
       [0012] Both the fixed differential (also known as an hypocycle) and the planetary gear set (also known as an epicycle) produce a single output that is a function of multiple inputs. There are several different types of fixed differentials or hypocycles (using different types of gears), but the most common use spur gears, annular gears, or bevel gears. All fixed differentials function similarly, with the most common arrangement having an input shaft attached to one gear (either spur, annular, or bevel) and an output shaft attached to the other gear (which is of the same type as the first). These two gears (the input gear and the output gear) are parallel, facially adjacent, and do not contact each other. The input gear and the output gear are linked by one or more planetary gears which orbit both the input and the output gears and tangentially contact both the input gear and the output gear. Generally, the input gear and the output gear differ in size (the number of teeth) to produce a gear ratio. Also, the planet gears can serve as an input into the fixed differential when they are connected to a driving member.  
       [0013] The planetary or epicyclic gear train gets its name from the resemblance to our solar system. A planetary gear set always includes a sun gear located in the center of the planetary gear set, one or more planet gears orbiting the sun gear, and a planet carrier or arm which links the planet gears. Often, it also includes an annular gear which encompasses the whole. Fundamentally, a planetary is a special type of epicyclic gear train in which one of the axes of gears may be in motion. The gear train discussed herein may be either simple or compound depending on the configuration of the planet member itself If the planet gear has two different gear faces, it is said to be a compound planetary. The theory of operation of the two types is the same, but generally the compound type is used for larger reduction ratios. Planetaries can be used in the design of computing mechanisms to predict a single output by summing two inputs to provide a single output.  
       [0014] A planetary gear set or fixed differential has two degrees of freedom. This means that the motion of each element of the mechanism is not defined unless the motion of two of its elements is specified. The important feature here is that the output is always the function of two inputs. During operation the inputs sometimes operate as outputs and outputs sometimes operate as inputs as in the case of an overrunning condition where the vehicle wheels are being driven instead of doing the driving (such as engine braking, in such cases there may be torque reversals within the system without changes in direction of rotation.) Generally, an AVRD is made by connecting a fixed differential or planetary gear set on each side of an open differential. There are several different ways that the components of an AVRD can be connected, with each producing some variation in the output, but basically the two variable outputs of the open differential are connected one to each of the planetary gear sets or fixed differentials (the open differential output can be used to drive any of the components of the planetary gear set or fixed differential) and the differential carrier is used as a second input into each planetary gear set or fixed differential. The effect is to allow for a variable ratio which produces the multiplying effect (channeling a multiple of the amount of torque available on the wheel that spins faster to the slower moving wheel so that the wheel with better traction gets more of the driving power from the engine). Thus, the system mechanically proportions torque according to the AVRD&#39;s phase shifts. A phase shift is the ability of the epicycle (fixed differential) or hypocycle (planetary sets) to operate concurrently (use multiple inputs), allowing the system of the Automatic Variable Ratio Differential to internally hesitate, stop, reverse, and create a source of motion, such as is introduced by the planet gear of the fixed differential (or planetary set) when the carrier revolves faster (or slower) than an axle sun gear, planetary carrier etc. This has the effect of varying the number of teeth in the sun or annular gears. This can affect the speed (ratio), torque, and internal direction of motion. This amounts to an infinitely variable (in torque and speed) pair of transmissions which operate complimentary to the standard open differential and to each other, to proportion both speed and torque (horsepower) between the wheels of a vehicle in response to variations in ground conditions.  
       [0015] There are multiple inputs into the Automatic Variable Ratio Differential. Any one or any combination of these inputs responds instantly to changes in relative speed among themselves, and causes the gear system to change phase relationship. Since the governing factor in this system is the path of least resistance, the corrections of torque and speed respond to changes in ground conditions as experienced separately by the tires and communicated to the system by the ground link of the two tires in a cooperative fashion.  
       [0016] A phase shift occurs in the system each time a driven gear changes its relative pitch diameter by increase of speed in the same relative direction as its prime mover (losing relative size) or slowing, stopping or reversing (gaining relative size) and vice versa. This is a process which resembles slippage, but does not slip.  
       [0017] It is this process which causes the system to seek the wheel which has traction and can accept the bulk of carrier torque and place it there at a reduced RPM, then begin to search for the maximum speed at which the wheel with traction can accept horsepower, even as it cooperates with changing ground conditions at the tire that was slipping, by communicating with the prime mover through the ground link.  
       [0018] The advantages of the automatic variable ratio differential are substantial. AVRDs perform the function of a standard differential (allowing the two drive axles to act as one when the vehicle is moving straight forward while allowing the two axles to spin at different speeds when the vehicle is turning) while eliminating the drawback of a vehicle becoming stuck when one wheel loses traction even when the other wheel does have traction. It channels torque to the wheel with traction so that the wheel with traction can pull the vehicle with multiples of the torque available to the slipping wheel. When the AVRD is used in conjunction with a brake that provides resistance to the slipping wheel axle, the wheel with traction can receive a great deal of torque due to the multiplying effect of the AVRD. The AVRD principle can also be used in the transfer case for a four-wheel-drive vehicle to improve the torque distribution to all four wheels. The AVRD also distributes torque shock throughout the system so that the axles can better handle the stresses. In addition, the AVRD can reduce the turning radius of a vehicle in certain configurations. This reduced turning radius results from the ability of some AVRD configurations to produce a reversing action on one wheel while the other continues forward. This produces a force couple which is a more effective means of turning. Also, because AVRDs prevent tire slippage and skidding, they reduce both tire wear and damage to the tire-surface interface. Additionally, in some configurations, AVRDs can act as a transmission for a vehicle. Finally, it should be noted that the principles of the AVRD can be used in devices other than vehicles. It can be used any time that multiple outputs are needed but several individual motors are impractical due to size constraints. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0019] Reference will be made to drawings wherein like parts in each preferred embodiment are designated by like numerals and wherein each figure illustrates a different preferred embodiment of the automatic variable ratio differential as described below.  
     [0020]FIG. 1 is a schematic of an embodiment of an AVRD.  
     [0021]FIG. 2 is a schematic of an embodiment of an AVRD.  
     [0022]FIG. 3 is a schematic of an embodiment of an AVRD.  
     [0023]FIG. 4 is a schematic of an embodiment of an AVRD.  
     [0024]FIG. 5 is a schematic of an embodiment of an AVRD.  
     [0025]FIG. 6 is a schematic of an embodiment of an AVRD.  
     [0026]FIG. 7 is a schematic of an embodiment of an AVRD.  
     [0027]FIG. 8 is a schematic of an embodiment of an AVRD.  
     [0028]FIG. 9 is a schematic of an embodiment of an AVRD.  
     [0029]FIG. 10 is a schematic of an embodiment of an AVRD.  
     [0030]FIG. 11 is a schematic of an embodiment of an AVRD.  
     [0031]FIG. 12 is a schematic of an embodiment of an AVRD.  
     [0032]FIG. 13 is a schematic of an embodiment of an AVRD.  
     [0033]FIG. 14 is a schematic of an embodiment of an AVRD.  
     [0034]FIG. 15 is a schematic of an embodiment of an AVRD.  
     [0035]FIG. 16 is a schematic of an embodiment of an AVRD which acts as a transmission.  
     [0036]FIG. 17 is a schematic of an embodiment of an AVRD which acts as a transmission. 
    
    
     BEST MODES FOR CARRYING OUT THE INVENTION  
     [0037] There are several different arrangements for the Automatic Variable Ratio Differential. The drawings are schematics which detail the several preferred embodiments. The size of each of the gears for any preferred embodiment will depend upon the use for which the device is designed, with the gear ratio being set according to the responsiveness of torque proportioning required for a particular use. Referring now to the drawings in detail, the first preferred embodiment of the AVRD is shown in the schematic labeled FIG. 1. This embodiment is comprised of an open differential  20  and two fixed differentials  40  and  50 . The input from the motor (not shown in the schematic) directs driving torque into the open differential  20 . On one side of the open differential  20 , the open differential output  29  is rigidly attached to the inner gear  41  of the fixed differential  40  (typically this is a spur type of gear, an annular type of gear, or a bevel type of gear). Facially adjacent to but not contacting the inner gear  41  is the outer gear  43  (which is the same type of gear as the inner gear  41 ). The outer gear  43  has more teeth than does the inner gear  41  of the fixed differential  40 . One or more planet gears  45  link the inner gear  41  and the outer gear  43  of open differential  40  by tangentially contacting both the inner gear  41  and the outer gear  43  with intermeshing teeth. Typically, there are two or three planet gears  45  spaced evenly about the gears that they contact (inner gear  41  and outer gear  43 ). Each of the planet gears  45  which tangentially contact the inner gear  41  and outer gear  43  in fixed differential  40  may vary in size along its length such that its diameter at the point of contact with the inner gear  41  is different than its diameter at the point of contact with the outer gear  43  in order to accommodate the difference in the number of teeth and in order to alter the ratio of the fixed differential  40 . The one or more planet gears  45  are rigidly attached to the open differential carrier  25 . If there are multiple planet gears  45  in fixed differential  40 , then the positions of the planet gears  45  are fixed relative to one another and relative to the open differential carrier  25  while allowing each planet gear  45  to rotate about its own center axis. If there is only one planet gear  45  in fixed differential  40 , then its position is fixed relative to the open differential carrier  25  while it is allowed to rotate about its center axis, and it is held in contact with the inner gear  41  and outer gear  43 . The fixed differential output  47  (which typically is an axle leading to a wheel) is rigidly attached to the outer gear  43  of the open differential  40 .  
     [0038] The other side of the AVRD is a mirror image of that described above. The open differential output  28  is rigidly attached to the inner gear  51  of the fixed differential  50  (typically this is a spur type of gear, an annular type of gear, or a bevel type of gear). Facially adjacent to but not contacting the inner gear  51  is the outer gear  53  (which is the same type of gear as the inner gear  51 ). The outer gear  53  has more teeth than does the inner gear  51  of the fixed differential  50 . One or more planet gears  55  link the inner gear  51  and the outer gear  53  of open differential  50  by tangentially contacting both the inner gear  51  and the outer gear  53  with intermeshing teeth. Typically, there are two or three planet gears  55  spaced evenly around the gears that they contact (inner gear  51  and outer gear  53 ). Each of the planet gears  55  which tangentially contact the inner gear  51  and outer gear  53  in fixed differential  50  may vary in size along its length such that its diameter at the point of contact with the inner gear  51  is different than its diameter at the point of contact with the outer gear  53  in order to accommodate the difference in the number of teeth and in order to alter the ratio of the fixed differential  50 . The one or more planet gears  55  are rigidly attached to the open differential carrier  25 . Thus, if there are a plurality of planet gears  55 , then the positions of the planet gears  55  are fixed relative to one another and relative to the open differential carrier  25  while allowing each planet gear  55  to rotate about its own center axis. If there is only one planet gear  55  in fixed differential  50 , then its position is fixed relative to the open differential carrier  25  while it is allowed to rotate about its center axis, and it is held in contact with the inner gear  51  and outer gear  53 . The fixed differential output  57  (which typically is an axle leading to a wheel) is rigidly attached to the outer gear  53  of the open differential  50 .  
     [0039] When the vehicle is traveling straight forward and both driving wheels have equal traction, the gears in both fixed differentials  40  and  50  act as though locked, and the entire AVRD rotates as a whole unit. If there is slipping, however, the gears in fixed differentials  40  and  50  will rotate relative to one another to channel the torque to the wheel with better traction. In this situation, the planet gears  45  in fixed differential  40  rotate around the center axis of fixed differential  40  at a different speed than the inner gear  41 , and so the planet gears  45  orbit the inner gear  41 . The outer gear  43  is simultaneously orbited by the planet gears  45 . Thus, the rotation and torque of the fixed differential output  47  is modified from the open differential output  29  by the relative motion of the planet gears  45  with respect to the inner gear  41  and by the difference in the number of teeth between inner gear  41  and outer gear  43 . Fixed differential  50  behaves similarly. The planet gears  55  in fixed differential  50  rotate around the center axis of fixed differential  50  at a different speed than the inner gear  51 , and so the planet gears  55  orbit the inner gear  51 . The outer gear  53  is simultaneously orbited by the planet gears  55 . Thus, the rotation and torque of the fixed differential output  57  is modified from the open differential output  28  by the relative motion of the planet gears  55  with respect to the inner gear  51  and by the difference in the number of teeth between inner gear  51  and outer gear  53 . When the AVRD functions as a whole, the driving torque coming into the open differential  20  is channeled to the wheel with better traction, with that wheel receiving a multiple of the torque that the slipping wheel can receive.  
     [0040] Another preferred embodiment of the AVRD is shown in the schematic labeled FIG. 2. This embodiment is comprised of an open differential  20  and two fixed differentials  40  and  50 . The input from the motor (not shown in the schematic) directs driving torque into the open differential  20 . On one side of the open differential  20 , the open differential output  29  is rigidly attached to the inner gear  41  of the fixed differential  40  (typically this is a spur type of gear, an annular type of gear, or a bevel type of gear). Facially adjacent to but not contacting the inner gear  41  is the outer gear  43  (which is the same type of gear as the inner gear  41 ). The outer gear  43  has less teeth than does the inner gear  41  of the fixed differential  40 . One or more planet gears  45  link the inner gear  41  and the outer gear  43  of open differential  40  by tangentially contacting both the inner gear  41  and the outer gear  43  with intermeshing teeth. Typically, there are two or three planet gears  45  spaced evenly about the gears that they contact (inner gear  41  and outer gear  43 ). Each of the planet gears  45  which tangentially contact the inner gear  41  and outer gear  43  in fixed differential  40  may vary in size along its length such that its diameter at the point of contact with the inner gear  41  is different than its diameter at the point of contact with the outer gear  43  in order to accommodate the difference in the number of teeth and in order to alter the ratio of the fixed differential  40 . The one or more planet gears  45  are rigidly attached to the open differential carrier  25 . If there are a plurality of planet gears  45 , then the positions of the planet gears  45  are fixed relative to one another and relative to the open differential carrier  25  while allowing each planet gear  45  to rotate about its own center axis. If there is only one planet gear  45  in fixed differential  40 , then its position is fixed relative to the open differential carrier  25  while it is allowed to rotate about its center axis, and it is held in contact with the inner gear  41  and outer gear  43 . The fixed differential output  47  (which typically is an axle leading to a wheel), is rigidly attached to the outer gear  43  of the open differential  40 .  
     [0041] The other side of the AVRD is a mirror image of that described above. The open differential output  28  is rigidly attached to the inner gear  51  of the fixed differential  50  (typically this is a spur type of gear, an annular type of gear, or a bevel type of gear). Facially adjacent to but not contacting the inner gear  51  is the outer gear  53  (which is the same type of gear as the inner gear  51 ). The outer gear  53  has less teeth than does the inner gear  51  of the fixed differential  50 . One or more planet gears  55  link the inner gear  51  and the outer gear  53  of open differential  50  by tangentially contacting both the inner gear  51  and the outer gear  53  with intermeshing teeth. Typically, there are two or three planet gears  55  evenly spaced around the gears that they contact (inner gear  51  and outer gear  53 ). Each of the planet gears  55  which tangentially contact the inner gear  51  and outer gear  53  in fixed differential  50  may vary in size along its length such that its diameter at the point of contact with the inner gear  51  is different than its diameter at the point of contact with the outer gear  53  in order to accommodate the difference in the number of teeth and in order to alter the ratio of the fixed differential  50 . The one or more planet gears  53  are rigidly attached to the open differential carrier  25 . If there are a plurality of planet gears  55  in planetary gear set  50 , then the positions of the planet gears  55  are fixed relative to one another and relative to the open differential carrier  25  while allowing each planet gear  55  to rotate about its own center axis. If there is only one planet gear  55  in fixed differential  50 , then its position is fixed relative to the open differential carrier  25  while it is allowed to rotate about its center axis, and it is held in contact with the inner gear  51  and outer gear  53 . The fixed differential output  57  (which typically is an axle leading to a wheel) is rigidly attached to the outer gear  53  of the open differential  50 .  
     [0042] Yet another preferred embodiment is shown in the schematic labeled FIG. 3. This embodiment is comprised of an open differential  20  and two planetary gear sets  40  and  50 . The input from the motor (not shown in the schematic) directs driving torque into the open differential  20 . On one side of the open differential  20 , the open differential output  29  rigidly connects to the sun gear  43  which is located in the center of the planetary gear set  40 . The open differential carrier  25  is rigidly attached to the annular gear  45  which encloses the planetary gear set  40 . The sun gear  43  and the annular gear  45  are both contacted (with intermeshing teeth) by one or more planet gears  47  which are located between the sun gear  43  and the annular gear  45 . Typically, there are two or three planet gears  47  spaced evenly around the sun gear  43 . If there are a plurality of planet gears  47 , then they are all joined by a planetary carrier  48  which rigidly fixes their positions relative to one another while allowing each planet gear  47  to rotate about its center axis. If there is only one planet gear  47  in planetary gear set  40 , then the planetary carrier  48 , which appears as a connecting arm, links the single planet gear  47  to the center axis of the planetary gear set  40  in order to hold the planet gear  47  in place while allowing the planet gear  47  to rotate about its center axis. The planetary carrier  48  is rigidly attached to the planetary gear set output  49  for planetary gear set  40 .  
     [0043] The other side of the AVRD is a mirror image of the side described above. The open differential output  28  rigidly connects to the sun gear  53  which is located in the center of the planetary gear set  50 . The open differential carrier  25  is rigidly attached to the annular gear  55  which encloses the planetary gear set  50 . The sun gear  53  and the annular gear  55  are both contacted (with intermeshing teeth) by one or more planet gears  57  which are located between the sun gear  53  and the annular gear  55 . Typically, there are two or three planet gears  57  spaced evenly around the sun gear  53 . If there are a plurality of planet gears  57 , then they are all joined by a planetary carrier  58  which rigidly fixes their positions relative to one another while allowing each planet gear  57  to rotate about its center axis. If there is only one planet gear  57  in planetary gear set  50 , then the planetary carrier  58 , which appears as a connecting arm, links the single planet gear  57  to the center axis of the planetary gear set  50  in order to hold the planet gear  57  in place while allowing the planet gear  57  to rotate about its center axis. The planetary carrier  58  is rigidly attached to the planetary gear set output  59  for planetary gear set  50 .  
     [0044] When the vehicle is traveling straight forward and both driving wheels have equal traction, the gears in both fixed differentials  40  and  50  act as though locked, and the entire AVRD rotates as a whole unit. If there is slipping, however, the gears in fixed differentials  40  and  50  will rotate relative to one another to channel the torque to the wheel with better traction. When this occurs, the planet gears  47  are acted upon by two different forces. The sun gear  43  attempts to pull the planet gears  47  along so that they rotate in step with it, while the annular gear  45  attempts to pull the planet gears  47  along so that they rotate in step with it. The result is that the planet gears  47  rotate as a unit around the center axis of planetary gear set  40  at their own speed and each planet gear  47  rotates about its own center axis to accommodate the difference. Thus, the rotation of the planetary carrier  48  is a function of the interplay between the sun gear  43 , the annular gear  45 , and the planet gears  47 . The behavior of planetary gear set  50  is similar. The planet gears  57  are acted upon by two different forces. The sun gear  53  attempts to pull the planet gears  57  along so that they rotate in step with it, while the annular gear  55  attempts to pull the planet gears  57  along so that they rotate in step with it. The result is that the planet gears  57  rotate as a unit around the center axis of planetary gear set  50  at their own speed and each planet gear  57  rotates about its own center axis to accommodate the difference. Thus, the rotation of the planetary carrier  58  is a function of the interplay between the sun gear  53 , the annular gear  55 , and the planet gears  57 . When the AVRD functions as a unit, the result is that the independent rotational motion of the gears in planetary gear sets  40  and  50  act to set up a ratio that channels the driving torque entering the open differential  20  to the wheel with better traction, sending it multiples of the torque available to the slipping wheel.  
     [0045] Yet another preferred embodiment is shown in the schematic labeled FIG. 4. This embodiment is comprised of an open differential  20  and two planetary gear sets  40  and  50 . The input from the motor (not shown in the schematic) directs driving torque into the open differential  20 . On one side of the open differential  20 , the sun gear  43  is located in the center of the planetary gear set  40  and is rigidly attached to the open differential carrier  25 . One or more planet gears  45  encircle the sun gear  43  and are in contact (with the teeth intermeshing) with the sun gear  43 . Typically, there are two or three planet gears  45  spaced evenly around the sun gear  43 . If there are a plurality of planet gears  45 , then they are rigidly linked by a planetary carrier  47  which fixes the positions of the planet gears  45  relative to one another while allowing each planet gear  45  to rotate about its center axis. If there is only one planet gear  45  in planetary gear set  40 , then the planetary carrier  47 , which appears as a connecting arm, links the single planet gear  45  to the center axis of the planetary gear set  40  in order to hold the planet gear  45  in place while allowing the planet gear  45  to rotate about its center axis. The open differential output  28  on this side is rigidly attached to the planetary carrier  47 . Encompassing the one or more planet gears  45  in this planetary gear set  40  is an annular gear  48 . This annular gear  48  makes contact with the one or more planet gears  45  such that the entire planetary gear set  40  is connected by the intermeshing teeth of the sun gear  43  with those on the one or more planet gears  45  and by the intermeshing teeth of the one or more planet gears  45  with those of the annular gear  48 . The annular gear  48  is rigidly attached to the planetary gear set output  49  for planetary gear set  40 .  
     [0046] The other side of the AVRD is a mirror image of the side described above. The sun gear  53  is located in the center of the planetary gear set  50  and is rigidly attached to the open differential carrier  25 . One or more planet gears  55  encircle the sun gear  53  and are in contact (with the teeth intermeshing) with the sun gear  53 . Typically, there are two or three planet gears  55  spaced evenly around the sun gear  53 . If there are a plurality of planet gears  55 , then they are rigidly linked by a planetary carrier  57  which fixes the positions of the planet gears  55  relative to one another while allowing each planet gear  55  to rotate about its center axis. If there is only one planet gear  55  in planetary gear set  50 , then the planetary carrier  57 , which appears as a connecting arm, links the single planet gear  55  to the center axis of the planetary gear set  50  in order to hold the planet gear  55  in place while allowing the planet gear  55  to rotate about its center axis. The open differential output  29  on this side is rigidly attached to the planetary carrier  57 . Encompassing the one or more planet gears  55  in this planetary gear set  50  is an annular gear  58 . This annular gear  58  makes contact with the one or more planet gears  55  such that the entire planetary gear set  50  is connected by the intermeshing teeth of the sun gear  53  with those on the one or more planet gears  55  and by the intermeshing teeth of the one or more planet gears  55  with those of the annular gear  58 . The annular gear  58  is rigidly attached to the planetary gear set output  59  for planetary gear set  50 . This configuration of the AVRD can reduce the turning radius of a vehicle in which an AVRD is installed due to the reactive force when the steering axle is aligned properly. This reduced turning radius results from the ability of this configuration of the AVRD to produce a reversing action on one wheel while the other continues forward.  
     [0047] Yet another preferred embodiment is shown in the schematic labeled FIG. 5. This embodiment is identical to that described above for FIG. 4 except that it additionally has a brake attached to each of the planetary carriers of the planetary gear sets. (While the preferred embodiment uses a brake, any type of rotary input may be used to alter the effect of the AVRD. Thus, any time in this document that the term “brake” is used, it is understood that it represents a wide array of possible rotary inputs). If engaged, a brake will act to retard the rotation of the planetary carrier to which it is attached, thereby acting as another input into the planetary gear set and altering the planetary gear set output from that planetary gear set. This embodiment is comprised of an open differential  20  and two planetary gear sets  40  and  50 . The input from the motor (not shown in the schematic) directs driving torque into the open differential  20 . On one side of the open differential  20 , the sun gear  43  is located in the center of the planetary gear set  40  and is rigidly attached to the open differential carrier  25 . One or more planet gears  45  encircle the sun gear  43  and are in contact (with the teeth intermeshing) with the sun gear  43 . Typically, there are two or three planet gears  45  spaced evenly around the sun gear  43 . If there are a plurality of planet gears  45 , then they are rigidly linked by a planetary carrier  47  which fixes the positions of the planet gears  45  relative to one another while allowing each planet gear  45  to rotate about its center axis. If there is only one planet gear  45  in planetary gear set  40 , then the planetary carrier  47 , which appears as a connecting arm, links the single planet gear  45  to the center axis of the planetary gear set  40  in order to hold the planet gear  45  in place while allowing the planet gear  45  to rotate about its center axis. Attached to the planetary carrier  47  is a brake  46  which, when disengaged, does not affect the rotation of the planetary carrier  47 , but when engaged, acts to retard the rotation of the planetary carrier  47 . The open differential output  28  on this side is rigidly attached to the planetary carrier  47 . Encompassing the one or more planet gears  45  in this planetary gear set  40  is an annular gear  48 . This annular gear  48  makes contact with the one or more planet gears  45  such that the entire planetary gear set  40  is connected by the intermeshing teeth of the sun gear  43  with those on the one or more planet gears  45  and by the intermeshing teeth of the one or more planet gears  45  with those of the annular gear  48 . The annular gear  48  is rigidly attached to the planetary gear set output  49  for planetary gear set  40 .  
     [0048] The other side of the AVRD is a mirror image of the side described above. The sun gear  53  is located in the center of the planetary gear set  50  and is rigidly attached to the open differential carrier  25 . One or more planet gears  55  encircle the sun gear  53  and are in contact (with the teeth intermeshing) with the sun gear  53 . Typically, there are two or three planet gears  53  evenly spaced about the sun gear  53 . If there are a plurality of planet gears  55 , then they are rigidly linked by a planetary carrier  57  which fixes the positions of the planet gears  55  relative to one another while allowing each planet gear  55  to rotate about its center axis. If there is only one planet gear  55  in planetary gear set  50 , then the planetary carrier  57 , which appears as a connecting arm, links the single planet gear  55  to the center axis of the planetary gear set  50  in order to hold the planet gear  55  in place while allowing the planet gear  55  to rotate about its center axis. A brake  56  is attached to the planetary carrier  57  such that, when disengaged, it does not affect the rotation of the planetary carrier  57 , but when engaged, it acts to retard the rotation of the planetary carrier  57 . The open differential output  29  on this side is rigidly attached to the planetary carrier  57 . Encompassing the one or more planet gears  55  in this planetary gear set  50  is an annular gear  58 . This annular gear  58  makes contact with the one or more planet gears  55  such that the entire planetary gear set  50  is connected by the intermeshing teeth of the sun gear  53  with those on the one or more planet gears  55  and by the intermeshing teeth of the one or more planet gears  55  with those of the annular gear  58 . The annular gear  58  is rigidly attached to the planetary gear set output  59  for planetary gear set  50 . This configuration of the AVRD can reduce the turning radius of a vehicle in which an AVRD is installed due to the application of brakes. This reduced turning radius results from the ability of this configuration of the AVRD to produce a reversing action on one wheel while the other continues forward.  
     [0049] Yet another preferred embodiment is shown in the schematic labeled FIG. 6. This embodiment is comprised of an open differential  20  and two planetary gear sets  40  and  50 . The input from the motor (not shown in the schematic) directs driving torque into the open differential  20 . On one side of the open differential  20 , the open differential carrier  25  is rigidly attached to the annular gear  41  of the planetary gear set  40 . In contact with the inner circumference of the annular gear  41  are one or more planet gears  43 . Typically there are two or three planet gears  43  spaced evenly around the annular gear&#39;s  41  inner circumference. The teeth of the one or more planet gears  43  intermesh with those of the annular gear  41 . If there are a plurality of planet gears  43 , then they are rigidly linked together by a planetary carrier  44  which fixes the position of the planet gears  43  relative to one another while allowing each planet gear  43  to rotate about its center axis. If there is only one planet gear  43  in planetary gear set  40 , then the planetary carrier  44 , which appears as a connecting arm, links the single planet gear  43  to the center axis of the planetary gear set  40  in order to hold the planet gear  43  in place while allowing the planet gear  43  to rotate about its center axis. The open differential output  29  on this side of the open differential  20  is rigidly attached to the planetary carrier  44  of the planetary gear set  40 . Also attached to the planetary carrier  44  is a brake  45  which, when disengaged, does not affect the rotation of the planetary carrier  44  but, when engaged, acts to retard the rotation of the planetary carrier  44 . Located centrally in the planetary gear set  40  is the sun gear  47 . The sun gear  47  is encircled and contacted by the one or more planet gears  43  such that the teeth of the sun gear  47  intermesh with those of the one or more planet gears  43  which are located around the circumference of the sun gear  47 . Thus, the planetary gear set  40  is made whole such that the motions of the components are interrelated due to the intermeshing of the teeth of the annular gear  41  with those of the one or more planet gears  43  and the intermeshing of the teeth of the one or more planet gears  43  with those of the sun gear  47 . The sun gear  47  is rigidly attached to the planetary gear set output  49  for planetary gear set  40 .  
     [0050] The other side of the AVRD is a mirror image of the side described above. The open differential carrier  25  is rigidly attached to the annular gear  51  of the planetary gear set  50 . In contact with the inner circumference of the annular gear  51  are one or more planet gears  53 . Typically there are two or three planet gears  53  spaced evenly around the annular gear&#39;s  51  inner circumference. The teeth of the one or more planet gears  53  intermesh with those of the annular gear  51 . If there are a plurality of planet gears  53 , then they are rigidly linked together by a planetary carrier  54  which fixes the position of the planet gears  53  relative to one another while allowing each planet gear  53  to rotate about its center axis. If there is only one planet gear  53  in planetary gear set  50 , then the planetary carrier  54 , which appears as a connecting arm, links the single planet gear  53  to the center axis of the planetary gear set  50  in order to hold the planet gear  53  in place while allowing the planet gear  53  to rotate about its center axis. The open differential output  28  on this side of the open differential  20  is rigidly attached to the planetary carrier  54  of the planetary gear set  50 . Also attached to the planetary carrier  54  is a brake  55  which, when disengaged, does not affect the rotation of the planetary carrier  54  but, when engaged, acts to retard the rotation of the planetary carrier  54 . Located centrally in the planetary gear set  50  is the sun gear  57 . The sun gear  57  is encircled and contacted by the one or more planet gears  53  such that the teeth of the sun gear  57  intermesh with those of the one or more planet gears  53  which are located around the circumference of the sun gear  57 . Thus, the planetary gear set  50  is made whole such that the motions of the components are interrelated due to the intermeshing of the teeth of the annular gear  51  with those of the one or more planet gears  53  and the intermeshing of the teeth of the one or more planet gears  53  with those of the sun gear  57 . The sun gear  57  is rigidly attached to the planetary gear set output  59  for planetary gear set  50 . This configuration of the AVRD can reduce the turning radius of a vehicle in which an AVRD is installed due to the application of brakes. This reduced turning radius results from the ability of this configuration of the AVRD to produce a reversing action on one wheel while the other continues forward.  
     [0051] Yet another preferred embodiment is shown in the schematic labeled FIG. 7. This embodiment is comprised of an open differential  20  and two planetary gear sets  40  and  50 . The input from the motor (not shown in the schematic) directs driving torque into the open differential  20 . On one side, the open differential output  29  rigidly attaches to the sun gear  41  which is located at the center of the planetary gear set  40 . The inner annular gear  42  of the planetary gear set  40  is rigidly attached to the open differential carrier  25  (and surrounds the sun gear  41 , leaving space between them for the one or more planetary gears  43 ). Located between and in contact (with intermeshing teeth) with the inner annular gear  42  and the sun gear  41  of the planetary gear set  40  are one or more planet gears  43 . Typically, there are two or more planet gears  43  evenly spaced surrounding the sun gear  41 . These one or more planet gears  43  extend out farther length-wise away from the open differential  20  than does the inner annular gear  42 . If there are a plurality of planet gears  43 , then they are rigidly linked by a planetary carrier  45  which fixes the position of the planet gears  43  relative to one another while allowing each planet gear  43  to rotate freely about its center axis. If there is only one planet gear  43  in planetary gear set  40 , then the planetary carrier  45 , which appears as a connecting arm, links the single planet gear  43  to the center axis of the planetary gear set  40  in order to hold the planet gear  43  in place while allowing the planet gear  43  to rotate about its center axis. A brake  47  is attached to the planetary carrier  45  of this planetary gear set  40  such that, when the brake  47  is engaged, it will retard the rotation of the planetary carrier  45 , but when the brake  47  is disengaged, it will have no affect on the rotation of the planetary carrier  45 . Located facially adjacent to but not making contact with the inner annular gear  42  of planetary gear set  40  is the outer annular gear  48 . Typically, the outer annular gear  48  has a different number of teeth than the inner annular gear  42 , and the one or more planet gears  43  which link them vary in size such that they have one diameter when contacting the inner annular gear  42  and a different diameter when contacting the outer annular gear  48 . The outer annular gear  48  contacts (with intermeshing teeth) the one or more planet gears  43  in this planetary gear set  40  on the portion of each of the planet gears  43  which extends beyond the inner annular gear  42 . The outer annular gear  48  is rigidly connected to the planetary gear set output  49  of planetary gear set  40 .  
     [0052] The other side of the AVRD is a mirror image of that described above. The open differential output  28  rigidly attaches to the sun gear  51  which is located at the center of the planetary gear set  50 . The inner annular gear  52  of the planetary gear set  50  is rigidly attached to the open differential carrier  25  (and surrounds the sun gear  51 , leaving space between them for the one or more planet gears  53 ). Located between and in contact (with intermeshing teeth) with the inner annular gear  52  and the sun gear  51  of the planetary gear set  50  are one or more planet gears  53 . Typically, there are two or three planet gears  53  evenly spaced surrounding the sun gear  51 . These one or more planet gears  53  extend out farther length-wise away from the open differential  20  than does the inner annular gear  52 . If there are a plurality of planet gears  53 , then they are rigidly linked by a planetary carrier  55  which fixes the position of the planet gears  53  relative to one another while allowing each planet gear  53  to rotate freely about its center axis. If there is only one planet gear  53  in planetary gear set  50 , then the planetary carrier  55 , which appears as a connecting arm, links the single planet gear  53  to the center axis of the planetary gear set  50  in order to hold the planet gear  53  in place while allowing the planet gear  53  to rotate about its center axis. A brake  57  is attached to the planetary carrier  55  of this planetary gear set  50  such that, when the brake  57  is engaged, it will retard the rotation of the planetary carrier  55 , but when the brake  57  is disengaged, it will have no affect on the rotation of the planetary carrier  55 . Located facially adjacent to but not making contact with the inner annular gear  52  of planetary gear set  50  is the outer annular gear  58 . Typically, the outer annular gear  58  has a different number of teeth than the inner annular gear  52 , and the one or more planet gears  53  which link them vary in size so that they have one diameter when contacting the inner annular gear  52  and a different diameter when contacting the outer annular gear  58 . The outer annular gear  58  contacts (with intermeshing teeth) the one or more planet gears  53  in this planetary gear set  50  on the portion of each of the planet gears  53  which extends beyond the inner annular gear  52 . The outer annular gear  58  is rigidly connected to the planetary gear set output  59  of planetary gear set  50 . This configuration of the AVRD can reduce the turning radius of a vehicle in which an AVRD is installed due to the application of brakes. This reduced turning radius results from the ability of this configuration of the AVRD to produce a reversing action on one wheel while the other continues forward.  
     [0053] Yet another preferred embodiment is shown in the schematic labeled FIG. 8. This embodiment is comprised of an open differential  20  and two planetary gear sets  40  and  50 . The input from the motor (not shown in the schematic) directs driving torque into the open differential  20 . On one side of the open differential  20 , the open differential output  29  is rigidly attached to the inner sun gear  41  which is located at the center of the planetary gear set  40 . The annular gear  42  acts to enclose the planetary gear set  40  and is rigidly attached to the open differential carrier  25 . Located between and in contact with the inner sun gear  41  and the annular gear  42  of the planetary set  40  are one or more planet gears  43 . There are typically two or three planet gears  43  spaced evenly around the inner sun gear  41 . If there are a plurality of planet gears  43 , then they are rigidly linked by a planetary carrier  45  which fixes the position of the planet gears  43  relative to one another while allowing each planet gear  43  to rotate about its own center axis. If there is only one planet gear  43  in planetary gear set  40 , then the planetary carrier  45 , which appears as a connecting arm, links the single planet gear  43  to the center axis of the planetary gear set  40  in order to hold the planet gear  43  in place while allowing the planet gear  43  to rotate about its center axis. In FIG. 8, the planetary carrier  45  fixes the position of the planet gears  43  not by connecting the center axes of the planet gears  43  but by locating a portion of the planet gears  43  which is smooth and not covered with teeth within holes in the planetary carrier  45 . The one or more planet gears  43  extend out farther lengthwise from the open differential  20  than does the inner sun gear  41 . A brake  47  is attached to the planet carrier  45  of the planetary gear set  40  such that, when the brake  47  is disengaged, it does not affect the motion of the planetary carrier  45 , but when the brake  47  is engaged, it acts to retard the rotation of the planetary carrier  45 . Located facially adjacent to but not making contact with the inner sun gear  41  of the planetary gear set  40  is the outer sun gear  48 . Typically, the outer sun gear  48  differs in size from the inner sun gear  41 , and the one or more planet gears  43  each vary in size such that their diameter when contacting the inner sun gear  41  is different than their diameter when contacting the outer sun gear  48  so that the size difference between the inner sun gear  41  and the outer sun gear  48  can be accommodated. The outer sun gear  48  contacts (with intermeshing teeth) the one or more planet gears  43  in this planetary gear set  40  on the portion of each of the planet gears  43  which extends beyond the inner sun gear  41 . It should be noted that the diameter of the one or more planet gears  43  may vary along their length so that the planet gears  43  mesh well with both the inner sun gear  41  and the outer sun gear  48  of the planetary gear set  40  even when the inner sun gear  41  and the outer sun gear  48  are sized differently (have different numbers of teeth). The outer sun gear  48  of the planetary gear set  40  is rigidly attached to the planetary gear set output  49  of the planetary gear set  40 .  
     [0054] The other side of the AVRD is a mirror image of the side described above. The open differential output  28  is rigidly attached to the inner sun gear  51  which is located at the center of the planetary gear set  50 . The annular gear  52  acts to enclose the planetary gear set  50  and is rigidly attached to the open differential carrier  25 . Located between and in contact with the inner sun gear  51  and the annular gear  52  of the planetary set  50  are one or more planet gears  53 . There are typically two or three planet gears  53  spaced evenly around the inner sun gear  51 . If there are a plurality of planet gears  53 , then they are rigidly linked by a planetary carrier  55  which fixes the position of the planet gears  53  relative to one another while allowing each planet gear  53  to rotate about its own center axis. If there is only one planet gear  53  in planetary gear set  50 , then the planetary carrier  55 , which appears as a connecting arm, links the single planet gear  53  to the center axis of the planetary gear set  50  in order to hold the planet gear  53  in place while allowing the planet gear  53  to rotate about its center axis. In FIG. 8, the planetary carrier  55  fixes the position of the planet gears  53  not by connecting the center axes of the planet gears  53  but by locating a portion of the planet gears  53  which is smooth and not covered with teeth within holes in the planetary carrier  55 . The one or more planet gears  53  extend out farther length-wise from the open differential  20  than does the inner sun gear  51 . A brake  57  is attached to the planet carrier  55  of the planetary gear set  50  such that, when the brake  57  is disengaged, it does not affect the motion of the planetary carrier  55 , but when the brake  57  is engaged, it acts to retard the rotation of the planetary carrier  55 . Located facially adjacent to but not making contact with the inner sun gear  51  of the planetary gear set  50  is the outer sun gear  58 . Typically, the outer sun gear  58  differs in size from the inner sun gear  51 , and the one or more planet gears  53  each vary in size such that their diameter when contacting the inner sun gear  51  is different than their diameter when contacting the outer sun gear  58  so that the size difference between the inner sun gear  51  and the outer sun gear  58  can be accommodated. The outer sun gear  58  contacts (with intermeshing teeth) the one or more planet gears  53  in this planetary gear set  50  on the portion of each of the planet gears  53  which extends beyond the inner sun gear  51 . It should be noted that the diameter of the one or more planet gears  53  may vary along their length so that the planet gears  53  mesh well with both the inner sun gear  51  and the outer sun gear  58  of the planetary gear set  50  even when the inner sun gear  51  and the outer sun gear  58  are sized differently (have different numbers of teeth). The outer sun gear  58  of the planetary gear set  50  is rigidly attached to the planetary gear set output  59  of the planetary gear set  50 . This configuration of the AVRD can reduce the turning radius of a vehicle in which an AVRD is installed due to the application of brakes. This reduced turning radius results from the ability of this configuration of the AVRD to produce a reversing action on one wheel while the other continues forward.  
     [0055] Yet another preferred embodiment is shown in the schematic labeled FIG. 9. This embodiment is comprised of an open differential  20  and two planetary gear sets  40  and  50 . The input from the motor (not shown in the schematic) directs driving torque into the open differential  20 . On one side of the open differential  20 , the open differential carrier  25  is rigidly attached to the annular gear  41  which acts to enclose the planetary gear set  40 . Located around the inner circumference of the annular gear  41  and in contact (with teeth intermeshing) with the annular gear  41  are one or more planet gears  45 . Typically there are two or three planet gears  45  spaced evenly around the inner circumference of the annular gear  41 . If there are a plurality of planet gears  45 , then they are rigidly linked together by a planetary carrier  47  which fixes the positions of the planet gears  45  relative to one another while allowing each planet gear  45  to rotate about its center axis. If there is only one planet gear  45  in planetary gear set  40 , then the planetary carrier  47 , which appears as a connecting arm, links the single planet gear  45  to the center axis of the planetary gear set  40  in order to hold the planet gear  45  in place while allowing the planet gear  45  to rotate about its center axis. A brake  49  is attached to the planetary carrier  47  of the planetary gear set  40  such that, when the brake  49  is disengaged, it has no affect on the rotation of the planet carrier  47 , but when the brake  49  is engaged, it acts to retard the rotation of the planetary carrier  47 . Located in the center of the planetary gear set  40  and orbited by and in contact with the one or more planet gears  45  is the sun gear  43  of planetary gear set  40 . Thus, the planetary gear set  40  is made whole as a unit by the sun gear  43  contacting the one or more planet gears  45  with intermeshing teeth and by the one or more planet gears  45  contacting the annular gear  41  with intermeshing teeth. The sun gear  43  of planetary gear set  40  rigidly attaches to the open differential output  29  and also to the planetary gear set output  44  of planetary gear set  40 .  
     [0056] The other side of the AVRD is a mirror image of that described above. The open differential carrier  25  is rigidly attached to the annular gear  51  which acts to enclose the planetary gear set  50 . Located around the inner circumference of the annular gear  51  and in contact (with teeth intermeshing) with the annular gear  51  are one or more planet gears  55 . Typically, there are two or three planet gears  55  spaced evenly around the inner circumference of the annular gear  51 . If there are a plurality of planet gears  55 , then they are rigidly linked together by a planetary carrier  57  which fixes the positions of the planet gears  55  relative to one another while allowing each planet gear  55  to rotate about its center axis. If there is only one planet gear  55  in planetary gear set  50 , then the planetary carrier  57 , which appears as a connecting arm, links the single planet gear  55  to the center axis of the planetary gear set  50  in order to hold the planet gear  55  in place while allowing the planet gear  55  to rotate about its center axis. A brake  59  is attached to the planetary carrier  57  of the planetary gear set  50  such that, when the brake  59  is disengaged, it has no affect on the rotation of the planet carrier  57 , but when the brake  59  is engaged, it acts to retard the rotation of the planetary carrier  57 . Located in the center of the planetary gear set  50  and orbited by and in contact with the one or more planet gears  55  is the sun gear  53  of planetary gear set  50 . Thus, the planetary gear set  50  is made whole as a unit by the sun gear  53  contacting the one or more planet gears  55  with intermeshing teeth and by the one or more planet gears  55  contacting the annular gear  51  with intermeshing teeth. The sun gear  53  of planetary gear set  50  rigidly attaches to the open differential output  28  and also to the planetary gear set output  54  of planetary gear set  50 . This configuration of the AVRD can reduce the turning radius of a vehicle in which an AVRD is installed due to the application of brakes. This reduced turning radius results from the ability of this configuration of the AVRD to produce a reversing action on one wheel while the other continues forward.  
     [0057] Yet another preferred embodiment is shown in the schematic labeled FIG. 10. This embodiment is comprised of an open differential  20  and two planetary gear sets  40  and  50 . The input from the motor (not shown in the schematic) directs driving torque into the open differential  20 . On one side, the open differential output  29  rigidly connects to the annular gear  41  of the planetary gear set  40  which rigidly connects to the planetary gear set output  42  of planetary gear set  40 . The sun gear  43  is located at the center of planetary gear set  40  and rigidly connects to the open differential carrier  25 . Located between and in contact with the annular gear  41  and the sun gear  43  of planetary gear set  40  are one or more planet gears  45  (said contact being the intermeshing of the teeth of the gears). Typically, there are two or three planet gears  45  evenly spaced about the sun gear. If there are a plurality of planet gears  45 , then they are rigidly linked together by a planetary carrier  47  which fixes the positions of the planet gears  45  relative to one another while allowing each planet gear  45  to rotate about its center axis. If there is only one planet gear  45  in planetary gear set  40 , then the planetary carrier  47 , which appears as a connecting arm, links the single planet gear  45  to the center axis of the planetary gear set  40  in order to hold the planet gear  45  in place while allowing the planet gear  45  to rotate about its center axis. A brake  49  attaches to the planetary carrier  47  of planetary gear set  40  such that, when the brake  49  is disengaged, it does not affect the rotation of the planetary carrier  47 , but when the brake  49  is engaged, it acts to retard the rotation of the planetary carrier  47 .  
     [0058] The other side of the AVRD is a mirror of the side described above. The open differential output  28  rigidly connects to the annular gear  51  of the planetary gear set  50  which rigidly connects to the planetary gear set output  52  of planetary gear set  50 . The sun gear  53  is located at the center of planetary gear set  50  and rigidly connects to the open differential carrier  25 . Located between and in contact with the annular gear  51  and the sun gear  53  of planetary gear set  50  are one or more planet gears  55  (said contact being the intermeshing of the teeth of the gears). Typically, there are two or three planet gears  55  spaced evenly around the sun gear  53 . If there are a plurality of planet gears, then they are rigidly linked together by a planetary carrier  57  which fixes the positions of the planet gears  55  relative to one another while allowing each planet gear  55  to rotate about its center axis. If there is only one planet gear  55  in planetary gear set  50 , then the planetary carrier  57 , which appears as a connecting arm, links the single planet gear  55  to the center axis of the planetary gear set  50  in order to hold the planet gear  55  in place while allowing the planet gear  55  to rotate about its center axis. A brake  59  attaches to the planetary carrier  57  of planetary gear set  50  such that, when the brake  59  is disengaged, it does not affect the rotation of the planetary carrier  57 , but when the brake  59  is engaged, it acts to retard the rotation of the planetary carrier  57 . This configuration of the AVRD can reduce the turning radius of a vehicle in which an AVRD is installed due to the application of brakes. This reduced turning radius results from the ability of this configuration of the AVRD to produce a reversing action on one wheel while the other continues forward.  
     [0059] Yet another preferred embodiment of the AVRD is shown in the schematic labeled FIG. 11. This embodiment is comprised of an open differential  20  and two planetary gear sets  40  and  50 . The input from the motor (not shown in the schematic) directs driving torque into the open differential  20 . On one side of the open differential  20 , the open differential output  29  rigidly attaches to the sun gear  41  located at the center of planetary gears set  40 . The sun gear  41  is encircled and contacted (with intermeshing teeth) by one or more planet gears  43 . Typically, there are two or three planet gears  43  spaced evenly around the sun gear  41 . If there are a plurality of planet gears  43  in planetary gear set  40 , then they are rigidly linked by the planetary carrier  45  of the planetary gears set  40  which fixes the position of the planet gears  43  relative to one another while allowing each planet gear  43  to rotate about its own center axis. If there is only one planet gear  43  in planetary gear set  40 , then the planetary carrier  45 , which appears as a connecting arm, links the single planet gear  43  to the center axis of the planetary gear set  40  in order to hold the planet gear  43  in place while allowing the planet gear  43  to rotate about its center axis. The planetary carrier  45  of planetary gear set  40  is rigidly attached to the open differential carrier  25 . The one or more planet gears  43  in planetary gear set  40  are encompassed by the annular gear  47  of planetary gear set  40 . The annular gear  47  makes contact with the one or more planet gears  43  with intermeshing teeth. Rigidly attached to the annular gear  47  of planetary gear set  40  is the planetary gear set output  49  (most often an axle which leads to a wheel).  
     [0060] The other side of the AVRD mirrors that described above. The open differential output  28  rigidly attaches to the sun gear  51  located at the center of planetary gears set  50 . The sun gear  51  is encircled and contacted (with intermeshing teeth) by one or more planet gears  53 . Typically, there are two or three planet gears  53  in planetary gear set  50  spaced evenly around the sun gear  51 . If there are a plurality of planet gears  53 , then they are rigidly linked by the planetary carrier  55  of the planetary gear set  50  which fixes the position of the planet gears  53  relative to one another while allowing each planet gear  53  to rotate about its own center axis. If there is only one planet gear  53  in planetary gear set  50 , then the planetary carrier  55 , which appears as a connecting arm, links the single planet gear  53  to the center axis of the planetary gear set  50  in order to hold the planet gear  53  in place while allowing the planet gear  53  to rotate about its center axis. The planetary carrier  55  of planetary gear set  50  is rigidly attached to the open differential carrier  25 . The one or more planet gears  53  in planetary gear set  50  are encompassed by the annular gear  57  of planetary gear set  50 . The annular gear  57  makes contact with the one or more planet gears  53  with intermeshing teeth. Rigidly attached to the annular gear  57  of planetary gear set  50  is the planetary gear set output  59  (most often an axle which leads to a wheel).  
     [0061] Yet another preferred embodiment of the AVRD is shown in the schematic labeled FIG. 12. It is an example of configurations of the AVRD which use multiple layers of planet gears surrounding the sun gear of the planetary gear set. Any AVRD arrangement could use multiple layers of planet gears in place of a single layer of planet gears, but the preferred embodiment is shown in FIG. 15. This embodiment is comprised of an open differential  20  and two planetary gear sets  40  and  50 . The input from the motor (not shown in the schematic) directs driving torque into the open differential  20 . On one side of the open differential  20 , the sun gear  41  which is located at the center of planetary gear set  40  is rigidly attached to the open differential carrier  25 . One or more inner planet gears  42  orbit the sun gear  41  of the planetary gear set  40  and make contact with the sun gear  41  (with intermeshing teeth). Typically there are two or three inner planet gears  42  evenly spaced about the sun gear  41 . If there are a plurality of inner planet gears  42 , then they are rigidly linked together by a planetary carrier  45  which fixes the position of the plurality of inner planet gears  42  with respect to one another while allowing each inner planet gear  42  to rotate about its center axis. If there is only one inner planet gear  42  in planetary gear set  40 , then the planetary carrier  45 , which appears as a connecting arm, links the single inner planet gear  42  to the center axis of the planetary gear set  40  in order to hold the inner planet gear  42  in place while allowing the inner planet gear  42  to rotate about its center axis. Located farther outward radially and encircling the one or more inner planet gears  42  are one or more outer planet gears  43 . There are the same number of outer planet gears  43  as there are inner planet gears  42  in planetary gear set  40 . These outer planet gears  43  contact the inner planet gears  42  (with intermeshing teeth). If there are a plurality of outer planet gears  43  in planetary gear set  40 , then they are rigidly linked together by the planet carrier  45  which fixes the position of the outer planet gears  43  relative to one another and relative to the inner planet gears  42  while allowing each outer planet gear  43  to rotate about its own center axis. If there is only one outer planet gear  43  in planetary gear set  40 , then the planetary carrier  45 , which appears as a connecting arm, links the single outer planet gear  43  to the center axis of the planetary gear set  40  and fixes its position relative to the inner planet gear  42  in order to hold the outer planet gear  43  in place in the planetary gear set  40  while allowing the outer planet gear  43  to rotate about its center axis. A brake  46  attaches to the planet carrier  45  such that, when disengaged, it does not affect the rotation of the planetary carrier  45 , but when engaged, it retards the rotation of the planetary carrier  45 . The open differential output  28  is rigidly attached to the planetary carrier  45 . The annular gear  47  of planetary gear set  40  encompasses the one or more outer planet gears  43 , making contact with the outer planet gears  43  with intermeshing teeth. Rigidly attached to the annular gear  47  is the planetary gear set output  49  of planetary gear set  40 .  
     [0062] The other side of the AVRD is a mirror image of that described above. The sun gear  51  which is located at the center of planetary gear set  50  is rigidly attached to the open differential carrier  25 . One or more inner planet gears  52  encircle the sun gear  51  of the planetary gear set  50  and make contact with the sun gear  51  (with intermeshing teeth). Typically, there are two or three inner planet gears  52  evenly spaced about the sun gear  51 . If there are a plurality of inner planet gears  52  in planetary gear set  50 , then they are rigidly linked together by aplanetary carrier  55  which fixes the position of the plurality of inner planet gears  52  with respect to one another while allowing each inner planet gear  52  to rotate about its center axis. If there is only one inner planet gear  52  in planetary gear set  50 , then the planetary carrier  55 , which appears as a connecting arm, links the single inner planet gear  52  to the center axis of the planetary gear set  50  in order to hold the inner planet gear  52  in place while allowing the inner planet gear  42  to rotate about its center axis. Located farther outward radially and orbiting the one or more inner planet gears  52  are one or more outer planet gears  53 . There are the same number of outer planet gears  53  in planetary gear set  50  as there are inner planet gears  52 . These outer planet gears  53  contact the inner planet gears  52  (with intermeshing teeth). If there are a plurality of outer planet gears  53 , then they are rigidly linked together by the planet carrier  55  which fixes the position of the outer planet gears  53  relative to one another and relative to the inner planet gears  52  while allowing each outer planet gear  53  to rotate about its own center axis. If there is only one outer planet gear  53  in planetary gear set  50 , then the planetary carrier  55 , which appears as a connecting arm, links the single outer planet gear  53  to the center axis of the planetary gear set  50  and fixes its position relative to the inner planet gear  52  in order to hold the outer planet gear  53  in place in the planetary gear set  50  while allowing the outer planet gear  53  to rotate about its center axis. A brake  56  attaches to the planet carrier  55  such that, when disengaged, it does not affect the rotation of the planetary carrier  55 , but when engaged, it retards the rotation of the planetary carrier  55 . The open differential output  29  is rigidly attached to the planetary carrier  55 . The annular gear  57  of planetary gear set  50  encompasses the one or more outer planet gears  53 , making contact with the one or more outer planet gears  53  (with intermeshing teeth). Rigidly attached to the annular gear  57  is the planetary gear set output  59  of planetary gear set  50 .  
     [0063] An AVRD can also be constructed using compound planetary gear sets on each side of the open differential. This may be useful when a high ratio is needed. A compound planetary gear setup can be made with any variety of gear connections between the open differential and the multiple planetary gear sets or fixed differentials on each side of the open differential, but the preferred embodiment is shown in the schematic labeled FIG. 13. This embodiment is comprised of an open differential  20  and four planetary gear sets  40 ,  50 ,  60 , and  70 . The input from the motor (not shown in the schematic) directs driving torque into the open differential  20 . On one side of the open differential  20 , the sun gear  41  located at the center of planetary gear set  40  rigidly attaches to the open differential carrier  25 . The sun gear  41  is orbited by one or more planet gears  43  which make contact with the sun gear  41  with intermeshing teeth. Typically, there are two or three planet gears  43  in planetary gear set  40  spaced evenly around the sun gear  41 . If there are a plurality of planet gears  43 , then they are rigidly linked together by a planetary carrier  45  which fixes the positions of the planet gears  43  relative to one another while allowing each planet gear  43  to rotate about its own center axis. If there is only one planet gear  43  in planetary gear set  40 , then the planetary carrier  45 , which appears as a connecting arm, links the single planet gear  43  to the center axis of the planetary gear set  40  in order to hold the planet gear  43  in place while allowing the planet gear  43  to rotate about its center axis. A brake  46  attaches to the planetary carrier  45  such that, when the brake  46  is disengaged, it has no affect on the rotation of the planetary carrier  45 , but when the brake  46  is engaged, it acts to retard the rotation of the planetary carrier  45 . Rigidly attached to the planetary carrier  45  of planetary gear set  40  is the open differential output  29 . The annular gear  47  of planetary gear set  40  encompasses the one or more planet gears  43  and contacts the one or more planet gears  43  with intermeshing teeth. Annular gear  47  of planetary gear set  40  is rigidly attached to the annular gear  61  of planetary gear set  60  (the outer planetary gear set on this side). Located around the inner circumference of the annular gear  61  of planetary gear set  60  are one or more planet gears  63 . These planet gears  63  make contact with the annular gear  61  with intermeshing teeth. Typically there are two or three planet gears  63  in planetary gear set  60  spaced evenly about the inner circumference of the annular gear  61 . If there are a plurality of planet gears  63  in planetary gear set  60 , then they are rigidly linked together by the planetary carrier  65  for planetary gear set  60  such that the position of the planet gears  63  are fixed relative to one another while allowing each planet gear  63  to rotate about its own center axis. If there is only one planet gear  63  in planetary gear set  60 , then the planetary carrier  65 , which appears as a connecting arm, links the single planet gear  63  to the center axis of the planetary gear set  60  in order to hold the planet gear  63  in place while allowing the planet gear  63  to rotate about its center axis. Attached to the planetary carrier  65  of planetary gear set  60  is a brake  66  which, when disengaged, does not affect the rotation of the planetary carrier  65 , but when engaged, acts to retard the rotation of the planetary carrier  65  of planetary gear set  60 . Located in the center of planetary gear set  60  and orbited by the one or more planet gears  63  is the sun gear  67  of planetary gear set  60 . The sun gear  67  contacts the one or more planet gears  63  with intermeshing teeth. Rigidly attached to the sun gear  67  of planetary gear set  60  is the planetary gear set output  69 .  
     [0064] The other side of the AVRD is a mirror image of that described above. The sun gear  51  located at the center of planetary gear set  50  rigidly attaches to the open differential carrier  25 . The sun gear  51  is encircled by one or more planet gears  53  which make contact with the sun gear  51  with intermeshing teeth. Typically, there are two or three planet gears  53  spaced evenly around the sun gear  51 . If there are a plurality of planet gears  53  in planetary gear set  50 , then they are rigidly linked together by a planetary carrier  55  which fixes the positions of the planet gears  53  relative to one another while allowing each planet gear  53  to rotate about its own center axis. If there is only one planet gear  53  in planetary gear set  50 , then the planetary carrier  55 , which appears as a connecting arm, links the single planet gear  53  to the center axis of the planetary gear set  50  in order to hold the planet gear  53  in place while allowing the planet gear  53  to rotate about its center axis. A brake  56  attaches to the planetary carrier  55  such that, when the brake  56  is disengaged, it has no affect on the rotation of the planetary carrier  55 , but when the brake  56  is engaged, it acts to retard the rotation of the planetary carrier  55 . Rigidly attached to the planetary carrier  55  of planetary gear set  50  is the open differential output  28 . The annular gear  57  of planetary gear set  50  encompasses the one or more planet gears  53  and contacts the planet gears  53  with intermeshing teeth. Annular gear  57  of planetary gear set  50  is rigidly attached to the annular gear  71  of planetary gear set  70  (the outer planetary gear set on this side). Located around the inner circumference of the annular gear  71  of planetary gear set  70  are one or more planet gears  73 . These planet gears  73  make contact with the annular gear  71  with intermeshing teeth. Typically, there are two or three planet gears  73  spaced evenly about the inner circumference of the annular gear  71 . If there are a plurality of planet gears  73  in planetary gear set  70 , then they are rigidly linked together by the planetary carrier  75  for planetary gear set  70  such that the position of the planet gears  73  are fixed relative to one another while allowing each planet gear  73  to rotate about its own center axis. If there is only one planet gear  73  in planetary gear set  70 , then the planetary carrier  75 , which appears as a connecting arm, links the single planet gear  73  to the center axis of the planetary gear set  70  in order to hold the planet gear  73  in place while allowing the planet gear  73  to rotate about its center axis. Attached to the planetary carrier  75  of planetary gear set  70  is a brake  76  which, when disengaged, does not affect the rotation of the planetary carrier  75 , but when engaged, acts to retard the rotation of the planetary carrier  75  of planetary gear set  70 . Located in the center of planetary gear set  70  and orbited by the one or more planet gears  73  is the sun gear  77  of planetary gear set  70 . The sun gear  77  contacts the planet gears  73  with intermeshing teeth. Rigidly attached to the sun gear  77  of planetary gear set  70  is the planetary gear set output  79 . This configuration of the AVRD can reduce the turning radius of a vehicle in which an AVRD is installed due to the application of brakes. This reduced turning radius results from the ability of this configuration of the AVRD to produce a reversing action on one wheel while the other continues forward.  
     [0065] An AVRD can also be used to allow for differentiation of multiple driving wheels in a linear alignment (for example, two wheels on each side of the open differential such as used on heavy trucks). This is accomplished by having a series of planetary gear sets or fixed differentials on each side of the open differential with a wheel attached to each planetary gear set or fixed differential, providing each wheel with independent speed and torque control abilities. Such an arrangement can be made by connecting planetary gear sets or fixed differentials in series, and there are several different ways that the actual connections can be setup, but the schematic in FIG. 14 shows the preferred embodiment. This embodiment is comprised of an open differential  20  and four planetary gear sets  40 ,  50 ,  60 , and  70 . The input from the motor (not shown in the schematic) directs driving torque into the open differential  20 . The sun gear  41  which is located in the center of planetary gear set  40  is rigidly attached to the open differential carrier  25  of the open differential  20 . The sun gear  41  is orbited by one or more planet gears  43  which make contact with the sun gear  41  with intermeshing teeth. Typically, there are two or three planet gears  43  spaced evenly around the sun gear  41 . If there are a plurality of planet gears  43  in planetary gear set  40 , then they are rigidly linked together by a planetary carrier  45  which fixes the position of the planet gears  43  relative to one another while allowing each planet gear  43  to rotate about its own center axis. If there is only one planet gear  43  in planetary gear set  40 , then the planetary carrier  45 , which appears as a connecting arm, links the single planet gear  43  to the center axis of the planetary gear set  40  in order to hold the planet gear  43  in place while allowing the planet gear  43  to rotate about its center axis. A brake  46  attaches to the planetary carrier  45  such that, when the brake  46  is disengaged, it does not affect the rotation of the planetary carrier  45 , but when the brake  46  is engaged, it acts to retard the rotation of the planetary carrier  45 . The one or more planet gears  43  are encompassed by the annular gear  47  of planetary gear set  40 , and the planet gears  43  make contact with the annular gear  47  with intermeshing teeth. The open differential output  29  on this side of the open differential  20  is rigidly attached to the planetary carrier  45  of planetary gear set  40  which is rigidly attached to the sun gear  61  of planetary gear set  60  (the outer planetary gear set on this side). In effect, the open differential output  29  connects first to the planetary carrier  45  of planetary gear set  40  and then extends out beyond planetary gear set  40  and into planetary gear set  60  to connect to the sun gear  61 . The sun gear  61  is located in the center of planetary gear set  60  and is encircled by one or more planet gears  63  which make contact with sun gear  61  with intermeshing teeth. Typically, there are two or three planet gears  63  spaced evenly around the sun gear  61 . If there are a plurality of planet gears  63  in planetary gear set  60 , then they are rigidly linked together by a planetary carrier  65  which fixes the position of the planet gears  63  relative to one another while allowing each planet gear  63  to rotate about its own center axis. If there is only one planet gear  63  in planetary gear set  60 , then the planetary carrier  65 , which appears as a connecting arm, links the single planet gear  63  to the center axis of the planetary gear set  60  in order to hold the planet gear  63  in place while allowing the planet gear  63  to rotate about its center axis. The planetary carrier  65  of planetary gear set  60  is rigidly attached to the annular gear  47  of planetary gear set  40  (the inner planetary gear set on this side). The one or more planet gears  63  of planetary gear set  60  are encompassed by the annular gear  67  of planetary gear set  60  such that the one or more planet gears  63  make contact with the annular gear  67  with intermeshing teeth. The attachment to the wheels is from each of the annular gears  47  and  67 .  
     [0066] The other side of the AVRD is a mirror image of that described above. The sun gear  51  which is located in the center of planetary gear set  50  is rigidly attached to the open differential carrier  25  of the open differential  20 . The sun gear  51  is encircled by a one or more planet gears  53  which make contact with the sun gear  51  with intermeshing teeth. Typically, there are two or three planet gears  53  in planetary gear set  50  spaced evenly around the sun gear  51 . If there are a plurality of planet gears  53 , then they are rigidly linked together by a planetary carrier  55  which fixes the position of the planet gears  53  relative to one another while allowing each planet gear  53  to rotate about its own center axis. If there is only one planet gear  53  in planetary gear set  50 , then the planetary carrier  55 , which appears as a connecting arm, links the single planet gear  53  to the center axis of the planetary gear set  50  in order to hold the planet gear  53  in place while allowing the planet gear  53  to rotate about its center axis. A brake  56  attaches to the planetary carrier  55  such that, when the brake  56  is disengaged, it does not affect the rotation of the planetary carrier  55 , but when the brake  56  is engaged, it acts to retard the rotation of the planetary carrier  55 . The one or more planet gears  53  are encompassed by the annular gear  57  of planetary gear set  50 , and the planet gears  53  make contact with the annular gear  57  with intermeshing teeth. The open differential output  28  on this side of the open differential  20  is rigidly attached to the planetary carrier  55  of planetary gear set  50  which is rigidly attached to the sun gear  71  of planetary gear set  70  (the outer planetary gear set on this side). In effect, the open differential output  28  connects first to the planetary carrier  55  of planetary gear set  50  and then extends out beyond planetary gear set  50  and into planetary gear set  70  to connect to the sun gear  71 . The sun gear  71  is located in the center of planetary gear set  70  and is orbited by one or more planet gears  73  which make contact with sun gear  71  with intermeshing teeth. Typically, there are two or three planet gears  73  spaced evenly around the sun gear  71 . If there are a plurality of planet gears  73  in planetary gear set  70 , then they are rigidly linked together by a planetary carrier  75  which fixes the position of the planet gears  73  relative to one another while allowing each planet gear  73  to rotate about its own center axis. If there is only one planet gear  73  in planetary gear set  70 , then the planetary carrier  75 , which appears as a connecting arm, links the single planet gear  73  to the center axis of the planetary gear set  70  in order to hold the planet gear  73  in place while allowing the planet gear  73  to rotate about its center axis. The planetary carrier  75  of planetary gear set  70  is rigidly attached to the annular gear  57  of planetary gear set  50  (the inner planetary gear set on this side). The one or more planet gears  73  of planetary gear set  70  are encompassed by the annular gear  77  of planetary gear set  70  such that the planet gears  73  make contact with the annular gear  77  with intermeshing teeth. The attachment to the wheels is from each of the annular gears  57  and  77 . This configuration of the AVRD can reduce the turning radius of a vehicle in which an AVRD is installed due to the application of brakes. This reduced turning radius results from the ability of this configuration of the AVRD to produce a reversing action on one wheel while the other continues forward.  
     [0067] In all configurations of the AVRD, an internal open differential carrier can be used instead of the external open differential carrier which is more commonly used. An example of such an embodiment using an internal open differential carrier is shown in the schematic labeled FIG. 15. This preferred embodiment is comprised of an open differential  20  and two planetary gear sets  40  and  50 . The input from the motor (not shown in the schematic) directs driving torque into the open differential  20 . On one side of the open differential  20 , the sun gear  41  which is located at the center of planetary gear set  40  is rigidly attached to the internal open differential carrier  25 . The sun gear  41  is encircled by one or more planet gears  43  which contact the sun gear  41  with intermeshing teeth. Typically, there are two or three planet gears evenly spaced about the sun gear  41 . If there are a plurality of planet gears  43  in planetary gear set  40 , then they are rigidly linked together by a planetary carrier  45  which fixes the positions of the planet gears  43  relative to one another while allowing each of the planet gears  43  to rotate about its own center axis. If there is only one planet gear  43  in planetary gear set  40 , then the planetary carrier  45 , which appears as a connecting arm, links the single planet gear  43  to the center axis of the planetary gear set  40  in order to hold the planet gear  43  in place while allowing the planet gear  43  to rotate about its center axis. The planetary carrier  45  of planetary gear set  40  is rigidly attached to the open differential output  29  and also to a brake  46 . When the brake  46  is disengaged, it does not affect the rotation of the planetary carrier  45 , but when the brake  46  is engaged, it acts to retard the rotation of the planetary carrier  45 . The one or more planet gears  43  of planetary gear set  40  are encompassed by the annular gear  47  of the planetary gear set  40 , and the one or more planet gears  43  make contact with the annular gear  47  with intermeshing teeth. The annular gear  47  is rigidly attached to the planetary gear set output  49  of planetary gear set  40 .  
     [0068] The other side of the AVRD is a mirror image of that described above. The sun gear  51  which is located at the center of planetary gear set  50  is rigidly attached to the internal open differential carrier  25 . The sun gear  51  is orbited by one or more planet gears  53  which contact the sun gear  51  with intermeshing teeth. Typically, there are two or three planet gears  53  evenly spaced about the sun gear  51 . If there are a plurality of planet gears  53  in planetary gear set  50 , then they are rigidly linked together by a planetary carrier  55  which fixes the positions of the planet gears  53  relative to one another while allowing each of the planet gears  53  to rotate about its own center axis. If there is only one planet gear  53  in planetary gear set  50 , then the planetary carrier  55 , which appears as a connecting arm, links the single planet gear  53  to the center axis of the planetary gear set  50  in order to hold the planet gear  53  in place while allowing the planet gear  53  to rotate about its center axis. The planetary carrier  55  of planetary gear set  50  is rigidly attached to the open differential output  28  and also to a brake  56 . When the brake  56  is disengaged, it does not affect the rotation of the planetary carrier  55 , but when the brake  56  is engaged, it acts to retard the rotation of the planetary carrier  55 . The one or more planet gears  53  of planetary gear set  50  are encompassed by the annular gear  57  of the planetary gear set  50 , and the one or more planet gears  53  make contact with the annular gear  57  with intermeshing teeth. The annular gear  57  is rigidly attached to the planetary gear set output  59  of planetary gear set  50 . This configuration of the AVRD can reduce the turning radius of a vehicle in which an AVRD is installed due to the application of brakes. This reduced turning radius results from the ability of this configuration of the AVRD to produce a reversing action on one wheel while the other continues forward.  
     [0069] The AVRD can also be made to function as a transmission for a vehicle by altering its configuration. One method for doing this involves replacing one of the planetary gear sets or fixed differentials with a variable speed motor. The planetary gear set or fixed differential which is used in this arrangement can be connected to the open differential in any of the configurations described above. The schematic in FIG. 16 shows the preferred embodiment for this arrangement. This embodiment is comprised of an open differential  20 , a fixed differential  40 , and a variable speed motor  50 . The variable speed motor  50  is rigidly attached to the open differential output  28  on one side of the open differential  20 . On the other side of the open differential  20 , the open differential output  29  is rigidly attached to the inner gear  41  of the fixed differential  40  (typically, it is a gear of the annular type, the spur type, or the bevel type). Facially adjacent to but not in contact with the inner gear  41  is the outer gear  43  of the fixed differential  40  (which is of the same gear type as the inner gear  41 ). The outer gear  43  has more teeth than does the inner gear  41 . One or more planet gears  45  link the inner gear  41  and the outer gear  43  of the fixed differential  40  by tangentially contacting both with intermeshing teeth. The one or more planet gears  45  are rigidly attached to the open differential carrier  25 . Typically, there are two or three planet gears  45  spaced evenly around the inner gear  41  and the outer gear  43 . If there a plurality of planet gears  45  in fixed differential  40 , then the positions of the planet gears  45  are fixed relative to one another and relative to the open differential carrier  25  while allowing each planet gear  45  to rotate about its own center axis. If there is only one planet gear  45  in fixed differential  40 , then its position is fixed relative to the open differential carrier  25  while it is allowed to rotate about its center axis, and it is held in contact with the inner gear  41  and outer gear  43 . The fixed differential output  47  is rigidly attached to the outer gear  43  of the fixed differential  40 .  
     [0070] Yet another preferred embodiment in which the AVRD can be used as a transmission is shown in the schematic labeled FIG. 17. On one side of the open differential  20 , the sun gear  55  is located in the center of planetary gear set  50 . A brake  56  attaches to the sun gear  55  such that, when disengaged, it does not affect the rotation of the sun gear  55 , but when engaged, it acts to retard the rotation of sun gear  55 . Orbiting sun gear  55  in planetary gear set  50  and in contact with sun gear  55  (with intermeshing teeth) are one or more planet gears  53 . Typically, there are two or three planet gears  53  evenly spaced around the sun gear. These planet gears  53  are rigidly attached to the side bevel gear  24  of the open differential  20  such that the positions of the planet gears  53  are fixed relative to each other and relative to the side bevel gear  24  while allowing each planet gear  53  to rotate about its own center axis. The one or more planet gears  53  are encompassed by the annular gear  51  of planetary gear set  50  and are in contact with the annular gear  51  (with intermeshing teeth). The annular gear  51  is rigidly attached to the carrier cross  25  of the open differential  20 . The carrier cross  25  passes through the open differential planet gears  26  and  27 , and the carrier cross  25  also passes through the input shaft  29  of the open differential  20 . Thus, when the input shaft  29  rotates, it causes the carrier cross  25  to move with it, and this causes the annular gear  51  of the planetary gear set  50  to rotate. The input shaft  29  passes through the side bevel gear  23  of the open differential  20  and connects (either rigidly or with keyed teeth) to the sun gear  41  of planetary gear set  40 . Sun gear  41  is encircled by one or more planet gears  43  which make contact with sun gear  41  (with intermeshing teeth). Typically, there are two or three planet gears  43  spaced evenly about the sun gear  41 . The planet gears  43  are rigidly attached to the side bevel gear  23  of the open differential  20  such that the positions of the planet gears  43  are fixed relative to one another and relative to the side bevel gear  23  while allowing each planet gear  43  to rotate about its own center axis. A brake  46  is attached to the side bevel gear  23  such that, when it is disengaged, the rotation of the side bevel gear  23  is not affected, but when the brake  46  is engaged, it acts to retard the rotation of the side bevel gear  23  and the planet gears  43 . Encompassing the one or more planet gears  43  of planetary gear set  40  is the annular gear  47 . The annular gear  47  makes contact on its inner surface (with intermeshing teeth) with the one or more planet gears  43 . Rigidly attached to the annular gear  47  is the transmission output  49  (which is typically a shaft).  
     INDUSTRIAL APPLICABILITY  
     [0071] The AVRD represents an improvement in vehicle differentials. Due to the widespread use of motorized vehicles (which incorporate differentials), the AVRD can have a broad impact industrially. In particular, it helps vehicles avoid becoming stuck in mud or ice. Thus, the AVRD is of benefit in any type of wheeled transportation industry, such as cargo transporting via trucks. Besides allowing such transportation to continue under severe conditions, the AVRD is also more durable than the limited-slip differentials currently used, so maintenance delays should be reduced. In addition, the AVRD allows for a much tighter vehicle turning radius in many of its configurations. This feature is particularly useful when vehicles are required to maneuver in close and confined quarters, such as forklifts moving items inside a warehouse. Because the vehicles which can benefit from the AVRD are used throughout many industries, the AVRD&#39;s industrial impact could be quite substantial.