NO-SLIP, IMPOSED DIFFERENTIAL

Abstract: A no-slip, imposed differential uses a first unlimited slip differential (15) connected for driving a pair of axle shafts (16) and (17) and a second unlimited slip differential (20) connected between a pair of control shafts (22) and (23). One of the axle shafts and one of the control shafts are connected for rotation in the same direction, and the other axle shaft and the other control shaft are connected for rotation in opposite directions. An input control gear (40) meshed with a ring gear (21) for second differential (20) can rotate control shafts (22) and (23) to impose differential rotation on axle shafts (16) and (17) via the shaft connecting means. This provides a no-slip drive when control gear (40) is not turning and a steering drive by imposed differential rotation when control gear (40) turns.

Description: TITLE NO-SLIP, IMPOSED DIFFERENTIAL BACKGROUND This invention arose from a search for a better way of steering track-laying vehicles, although the resulting discoveries also apply to many types of wheeled vehicles. Track-laying vehicles such as tractors are steered by a clutch and brake system that can unclutch the power to one track and brake one track while another track drives. Such arrangements are expensive and troublesome for many reasons, however. For example, disconnecting power to the left track of a tractor running on level ground tends to make the tractor turn left because the driving right track outdistances the left, but doing the same thing when the tractor is running downhill tends to make it turn right because the engine holds the right track back while the left rolls free. Braking tracks to slow down tends to straighten the line of travel so drivers must guard against braking on curves. Also, the sharpest turn a track-laying vehicle can make is by braking one track while driving the other, and this stresses the braked track considerably. In searching for a better solution for these and other problems, we have discovered a way of imposing differential rotation on axle shafts for steering both tracklaying and wheeled vehicles. Our imposed differen¬ tial can simultaneously drive wheels or tracks forward on one side of a vehicle and backward on the other side to allow pivot turns around a central point without overly stressing tracks or wheels. Our discovery also provides a no-slip differential that drives both sides of a vehicle regardless of relative traction and applies more power to the side with the greater traction. Our invention also leads to an improvement in wheel dynamometers for testing drive axles. It allows differential rotation to be imposed realistically on axle shafts under load. Our invention also accomplishes these advances by combining inexpensive and well-known components in ways that produce improved results. SUMMARY OF THE INVENTION Our no-slip, imposed differential uses a first unlimited slip differential connected for driving a pair of axle shafts and a second unlimited slip differential connected between a pair of control shafts. One of the control shafts is connected to one of the axle shafts for rotation in the same direction, and the other control shaft is connected to the other axle shaft for rotation in opposite directions. An input control gear meshed with a ring gear for the second differential can turn to rotate the control shafts and impose differential rotation on the axle shafts via the shaft connecting means. One wheel or track cannot slip in response to light traction because the axle shafts are geared together through the second differential. The control gear is preferably a worm gear, and the ring gear for the second differential is prefer¬ ably a worm wheel. Turning the control gear steers the vehicle because of the differential rotation this imposes on the vehicle's axle shafts driving wheels or tracks on opposite sides of the vehicle. DRAWINGS Figure 1 is a partially schematic view of a preferred embodiment of a no-slip, imposed differential according to our invention; Figure 2 is a partially schematic view of our imposed differential applied to a wheel dynamometer; and Figure 3 is a schematic view of a vehicle pivot turn made possible by our imposed differential. DETAILED DESCRIPTION An explanation of the operation and advantages of our invention follows a description of the basic preferred structure or configuration of our no-slip, imposed differ¬ ential as best shown in FIGS. 1 and 2. STRUCTURE As applied to a vehicle as shown in FIG. 1, engine power input via shaft 11 turning gear 12 rotates ring gear 13 and case 14 of a conventional, unlimited slip differential 15 connected for driving a pair of axle shafts 16 and 17 on opposite sides of the vehicle. Differential 15 is generally known and well understood in the power transmission art and is suitably sized to the vehicle being driven. This can range from small garden tractors and tillers up to large tractors and earth movers. Differential 15 is preferably a bevel gear differential lacking any limited slip devices so as not to impair differential rotation of axle shafts 16 and 17. A second differential 20, also of a conventional unlimited slip design, is connected between a pair of control shafts 22 and 23 that are interconnected in a driving relationship with axle shafts 16 and 17. One control shaft 23 and one axle shaft 17 are connected for rotation in the same direction, and another control shaft 22 and another axle shaft 16 are connected for rotation in opposite directions. This causes counter or differential rotation of control shafts 22 and 23 as axle shafts 16 and 17 rotate in the same direction and conversely causes differential rotation of axle shafts 16 and 17 as control shafts 22 and 23 rotate in the same direction. Gear connections between control shafts and axle shafts as shown in FIG. 1 are preferred for larger and more powerful vehicles. These include axle shaft gears 26 and 27 fixed respectively to axle shafts 16 and 17 and control shaft gears 32 and 33 fixed respectively to control shafts 22 and 23. Meshing axle shaft gear 26 with control shaft gear 32 provides opposite rotation between axle shaft 16 and control shaft 22, and meshing both axle shaft gear 27 and control shaft gear 33 with idler gear 25 provides same direction rotation for axle shaft 17 and control shaft 23. Gear connections between control shafts and axle shafts are preferably incorporated into an enlarged housing containing both axle differential 15 and control differential 20. For a reason explained below, control differential 20 can be sized to bear half the force borne by axle differential 15 so that the complete assembly can be fitted within a differential housing that is not unduly large. Smaller or less powerful vehicles can use shaft interconnections such as belts or chains in place of gearing. Also, shaft interconnections need not be limited to the region of the axle differential and can be made toward the outer ends of the axle shafts. A gear or drive ratio between control shafts and axle shafts is preferably 1:1. This ratio can vary, however, so long as it is the same on opposite sides of the axle and control differentials. An input control gear 40 meshes with a ring gear 21 of control differential 20 for imposing differential rotation on the system. Gear 40 is preferably a worm gear, and ring gear 21 is preferably a worm wheel so that ring gear 21 turns only when gear 40 turns. Gear 40 can be turned by several mechanisms, depending on the objective. For steering purposes, gear 40 can be turned by a steering shaft joined to control gear 40 and manually turned by a driver. Steering mechanisms can also use motors for turning gear 40. Alternatives include a DC starter motor 41 electrically turned via a rheostat in a steering system and a hydraulic or pneumatic motor turned by a vehicle's hydraulic or pneumatic system in response to a steering control. Our invention can also be applied to a wheel dynamometer 50 as schematically shown in FIG. 2. For such purpose, the drive axle 51 being tested by the dynamometer provides axle shafts 16 and 17 and axle differential 15, which need not be an unlimited slip differential and can be a no-slip differential such as disclosed in U.S. Patent No. 2,859,641. Power applied via input shaft 11 turns axle shafts 16 and 17, which can be subjected to varying loads by wheel dynamometer 50. Previous wheel dynamometers have caused differ- ential rotation of axle shafts 16 and 17 by subjecting them to different loads. This will not work with the differential of U.S. Patent No. 2,859,641, which applies more power to the more heavily loaded axle shaft. Our invention can apply differential rotation directly and realistically to axle shafts 16 and 17 via control differential 20 and its control shafts 22 and 23. These are connected to axle shafts 16 and 17 for same and opposite direction rotation as explained above; and when turned by control gear 40 rotated by motor 41, control shafts 22 and 23 impose differential rotation on axle shafts 16 and 17. Several drive interconnections are possible between the control shafts and the axle shafts of the test axle mounted on wheel dynamometer 50. One preferred arrangement shown in FIG. 2 uses meshed gears 26 and 32 fixed respectively to test axle shaft 16 and control shaft 22 for opposite direction rotation. Sprockets 57 and 53, coupled by a chain 54 and fixed respectively to test axle shaft 57 and control shaft 23, provide same direction rotation. Belts and other gearing arrangements are also possible. OPERATION Two important effects occur from the intercon¬ nection of control differential 20 and its control shafts 22 and 23 with axle differential 15 and axle shafts 16 and 17. One is a no-slip drive that prevents wheels or tracks from slipping unless slippage occurs on both sides of the vehicle at once. The other effect is imposed differential rotation that can accomplish steering to pivot or turn a vehicle. OMPI ^ The no-slip drive occurs because axle shafts 16 and 17 are geared together via differential 20. Power applied to an axle shaft on a side of the vehicle that has lost traction is transmitted to the connecting control shaft on that side, through differential 20 to the opposite control shaft, and back to the opposite axle shaft where it is added to the side having traction. So if one axle shaft loses traction, the opposite axle shaft drives harder; and the only way slippage can occur is if both axle shafts lose traction simultaneously. To elaborate on this, consider a vehicle rolling straight ahead with its axle shafts 16 and 17 turning uniformly in the same direction. Control gear 40 is stationary for straight ahead motion; and since control gear 40 is preferably a worm gear, worm wheel 21 of control differential 20..cannot turn. Control shafts 22 and 23, by their driving connections with the axle shafts, rotate differentially in opposite directions, which control differential 20 accommodates. Axle differential 15 equally divides the power input from shaft 11 and applies one-half of the input power to each axle shaft 16 and 17. If the track or wheel being driven by axle shaft 16 loses traction, it cannot apply the power available on shaft 16 and tends to slip. Actual slippage cannot occur, however, because axle shaft 16 is geared to control shaft 22. So if a wheel or track without traction cannot apply the power on shaft 16, this is transmitted to control shaft 22, which rotates in an opposite direction from axle shaft 16. Since ring gear 21 cannot turn, rotational power on control shaft 22 is transmitted through differential 20 to produce opposite rotation of control shaft 23. This is geared to axle shaft 17 via idler gear 25 so that power on control shaft 23 is applied to axle shaft 17 to urge shaft 17 in a forward direction driving the wheel or track that has traction and can accept the available power. Since only one-half of the full available power can be transmitted from one axle shaft to another via differential 20 and its control shafts, these can be sized to bear one-half the force borne by axle differential 15 and its axle shafts. Of course, unusable power available on axle shaft 17 because of a loss of traction on that side of the vehicle is transmitted through the same control shaft and control differential route to opposite axle shaft 16. This arrangement applies the most power to the wheel or track having the best traction, which is ideal for advancing the vehicle. The wheel or track that has lost traction will maintain rolling engagement with the ground while the other wheel or track drives. The only time wheels or tracks can slip is when they both lose traction simultaneously. To impose differential rotation on axle shafts 16 and 17 for pivoting or .turning the vehicle, it is only necessary to rotate control gear 40. This differentially rotates axle shafts to turn or pivot the vehicle because of the different distances traveled by the differentially rotating wheels or tracks on opposite sides of the vehicle. Steering controlled by rotating gear 40 can be applied to track-laying vehicles and wheeled vehicles that steer without using turning wheels. It can also be used for differentially rotating drive wheels or tracks to provide power-assisted steering for a vehicle that also has turning wheels. Whenever control gear 40 turns, it rotates ring gear 21, which turns the casing of differential 20 to rotate control shafts 22 and 23 in the same direction. The connection of control shafts 22 and 23 with axle shafts 16 and 17 converts the same direction rotation of control shafts 22 and 23 to opposite differential rotation of axle shafts 16 and 17, as accommodated by axle differential 15. This drives wheels or tracks forward on one side of the vehicle and rearward on the other side of the vehicle, depending on the direction of rotation of control gear 40. Such differential rotation is added to whatever forward or rearward rotation of the axle shafts is occurring at the time. So if a vehicle is moving forward or backward when control gear 40 turns, the differential rotation advances and retards opposite axle shafts and makes the vehicle turn. If a vehicle is not otherwise moving when control gear 40 turns, wheels or tracks go forward on one side and backward on the other side so that the vehicle pivots on a central point. This is schematically illustrated in FIG. 3 for a vehicle having a pair of tracks 75 and 76. Both tracks can have a rolling engagement with the ground as the vehicle rotates around a center point 77 by driving right track 76 forward and left track 75 rearward. The tracks experience some heel and toe scuffing, but this is less stress than if one track were braked still and the other driven. The pivot turn also spins the vehicle on one point 77, without requiring motion in any direction as must occur when one track is braked and another is driven. Pivot turns can also be made with wheeled vehicles, such as tractors, loaders, forklifts, etc. Many of these now have turning wheels that could advantageously, be replaced by non-turning wheels steered by imposed differential rotation according to our invention. To accommodate such vehicles, our invention can be applied to more than one drive axle powering more than one pair of drive wheels. Evidence indicates that pivot-turning capability can save considerable time for loaders, tractors, and forklifts compared to turning patterns requiring forward and rearward motion.

Claims: We claim: 1. A no-slip, imposed differential comprising: a. an unlimited slip drive differential connected for dividing driving torque between a pair of axle shafts; b. an unlimited slip control differential connected for dividing control torque between a pair of control shafts; c. axle shaft gears fixed to each of said axle shafts; d. control shaft gears fixed to each of said control shafts; one of said axle shaft gears being meshed with one of said control shaft gears; and an idler gear meshed with another one of said axle shaft gears and another one of said control shaft gears, whereby control torque rotating said control shafts imposes differential rotation on said axle shafts via said control gears, said idler gear, and said axle shaft gears, 2. The no-slip, imposed differential of claim 1 wherein said control differential is sized to bear half the force borne by said drive differential. 3. The no-slip, imposed differential of claim 1 including a steering mechanism providing said control torque. 4. The no-slip, imposed differential of claim 3 wherein said steering mechanism turns a worm gear input to said control differential. 5. A no-slip, imposed differential comprising: a. an unlimited slip drive differential connected for driving a pair of axle shafts; b. an unlimited slip control differential connected between a pair of control shafts; c. means for connecting one of said axle shafts and one of said control shafts for rotation in the same direction; and Λ REA OMPI d. means for connecting another one of said axle shafts and another one of said control shafts for rotation in opposite directions, whereby torque input to said control differential rotates said control shafts to impose differential rotation on said axle shafts via said shaft connecting means. 6. The no-slip, imposed differential of claim 5 wherein said torque input to said control differential is a worm gear and a worm wheel. 7. The no-slip, imposed differential of claim 5 wherein said control differential is sized to bear half the force borne by said first differential. 8. The no-slip, imposed differential of claim 5 including a steering mechanism for inputting torque to said control differential. 9. A wheel dynamometer for testing a drive axle driven through a differential connected to drive a pair of axle shafts subjected to variable loads, said dynamometer comprising: a. an unlimited slip control differential connected between a pair of control shafts; b. means for connecting one of said control shafts to one of said axle shafts for rotation in the same direction; and c. means for connecting another one of said control shafts to another one of said axle shafts for rotation in opposite directions, so that torque input to said control differential rotates said control shafts to impose differential rotation on said axle shafts via said shaft connecting means. 10. The wheel dynamometer of claim 9 wherein an endless drive means connects said one axle shaft and said one control shaft for rotation in the same direction. 11. The wheel dynamometer of claim 9 wherein a gear fixed to said other axle shaft meshes with a gear fixed to said other control shaft for rotation in opposite directions. f m $W, I 12. The wheel dynamometer of claim 9 wherein said torque input to said control differential includes a worm gear and a worm wheel. 13. A method of imposing no-slip differential rotation on a pair of drive axles, said method comprising: a. inputting driving torque to an unlimited-slip driving differential connected between said drive axles; b. inputting steering torque to an unlimited-slip steering differential connected between a pair of control shafts; c. connecting one of said control shafts and one of said drive axles for rotating in the same direction; and d. connecting the other of said control shafts and the other of said drive axles for rotating in opposite directions. 14. The method of claim 13 including sizing said steering differential to bear one-half the force borne by said first differential. 15. The method of claim 13 including using a worm and worm wheel for inputting said steering torque to said steering differential. 16. A vehicle steer driving method comprising: a. applying driving torque to vehicle axles via an unlimited-slip driving differential; b. applying steering torque to an unlimited-slip steering differential connected between a pair of control shafts; c. connecting one of said control shafts and one of said drive axles for rotating in the same direction; and d. connecting the other control shaft and the other drive axle for rotating in opposite directions. OMPI _ 17. A steering system for a vehicle having differentially driven drive axles, said system comprising: a. an unlimited-slip control differential connected between a pair of control shafts; b. means for applying steering torque to rotate said control differential and said control shafts; and c. said control shafts being connected to said drive axles so that rotation of said control shafts in the same direction rotates said drive axles in opposite directions. 18. The system of claim 17 including using a steering motor that can turn, but cannot be turned by, said control differential for inputting said steering torque to said control differential. 19. A vehicle steer drive system comprising: a. a driving differential for dividing driving torque; b. a steering differential for dividing steering torque; and c. divided torque outputs from said driving and steering differentials being combined additively on one side of said vehicle and subtractively on an opposite side of said vehicle to produce no-slip steer driving torque divided between right and left sides of said vehicle. 20. The system of claim 19 including a steering mechanism that can turn, but cannot be turned by, said steering differential for inputting said steering torque to said steering differential. 21. The system of claim 19 wherein said steering differential is sized to bear half the force borne by said driving differential. 22. A vehicle steer driving method comprising: a. 1 inputting driving torque to a driving differential; b. inputting steering torque to a steering differential; and c. combining the divided outputs of said driving and steering differentials additively on one side of said vehicle and subtractively on another side of said vehicle to prodlice no-slip, steer driving torque divided between right and left sides of said vehicle. 23. The method of claim 22 including using unlimited-slip differentials for said driving and steering differentials and sizing said steering differential to bear one-half the force borne by said driving differential. 24. The method of claim 22 including using a steering motor that can turn, but cannot be turned by, said control differential for inputting said steering torque to said control differential. 25. A vehicle steer driving method comprising: a. differentiating driving torque between opposite sides of said vehicle; b. dividing steering torque between opposite sides of said vehicle; and c. combining said steering and driving torques additively on on'e side of said vehicle and subtractively on the other side of said vehicle. 26. A vehicle steer drive system comprising: a. combining the outputs of a pair of unlimited- slip differentials additively on one side of said vehicle and subtractively on another side of said vehicle; and b. using one of said differentials to divide driving torque and the other of said differentials to divide steering torque. OMPI 27. A vehicle steer drive system comprising: a. a pair of unlimited-slip differentials having outputs connected additively on one side of said vehicle and subtractively on the other side of said vehicle; b. means for inputting driving torque to one of said differentials; and c. means for inputting steering torque to another one of said differentials. 28. The system of claim 27 including a steering mechanism that can turn, but cannot be turned by, said steering differential for inputting said steering torque to said steering differential.

Inventors: GLEASMAN JAMES Y, GLEASMAN KEITH E, GLEASMAN VERNON E, GLEASMAN, JAMES, Y., GLEASMAN, KEITH, E., GLEASMAN, VERNON, E.
Applicants: GLEASMAN JAMES Y, GLEASMAN KEITH E, GLEASMAN VERNON E, GLEASMAN, JAMES, Y., GLEASMAN, KEITH, E., GLEASMAN, VERNON, E.
Application year: 1984
Main classification: F16H37
IPC codes: B62D11, F16H37, F16H48