US1716073A | 1929-06-04 | |||
US3021725A | 1962-02-20 | |||
US3053404A | 1962-09-11 | |||
US3343620A | 1967-09-26 | |||
US4709775A | 1987-12-01 |
1. | A differential comprising: a) an input shaft; b) an output shaft coaxial with said input shaft; c) a differential case mounted for coaxial rotation about said input shaft; d) means rotatably supporting said differential case; e) a first external gear coaxial with and connected to said input shaft; f) means for rotatably supporting said first external gear within said differential case; g) a first internal gear cooperating with said first external gear and rotatable about an axis fixed relative to said differential case and parallel to and offset from the axis of said input shaft; h) a second external gear mounted coaxially with and rotationally connected to said first internal gear; i) means rotatably supporting said first internal gear and said second external gear within said differential case; j) a second internal gear cooperating with said second external gear mounted coaxially with and rotationally connected to said output shaft; k) means rotatably supporting said second internal gear within said differential case; and 1) coupling means ,by which torque may be transferred to or from said differential case. |
2. | The differential of claim 1 wherein said coupling means comprises a gear mounted coaxially with and rotatably connected to said differential case. |
3. | The differential of claim 1 wherein each external gear has at least 5 and less than 7 fewer teeth than its cooper¬ ating internal gear. |
4. | The differential of claim 1 wherein said first inter nal gear and said second external gear are mounted on a common hollow shaft rotatable about an axis parallel to and offset from the axis of said input shaft. |
5. | The differential of claim 4 wherein said output shaft is hollow and said input shaft is mounted coaxially and concentrically within said output shaft. |
6. | The differential of claim 5 wherein said parallel shaft is hollow and said input shaft extends through said parallel shaft. |
7. | The differential of claim 1 wherein said means for supporting said differential case comprises a vehicle frame. |
8. | A vehicle comprising a source of rotational power, two or more wheels and the differential of claim 1. |
9. | A driveline for a vehicle comprising two driving wheels, said driveline comprising a differential of the type described in claim 1 associated with each of said driving wheels, and wherein said coupling means of each said differential ,are connected by coupling gear means. |
10. | The driveline of claim 9 further comprising spin control brake means adapted for acting variably on said differential case of one of said differentials. |
11. | A driveline for a vehicle comprising two driving wheels, said driveline comprising a differential of the type described in claim 1 associated with each of said driving wheels, and wherein said coupling means of each said differential are connected by coupling gear means, further comprising a traction control torque generator, said traction control torque gener¬ ator comprising: a) "a bidirectional hydraulic motor having an output shaft and a first and second motor fluid port; b) a fourway hydraulic valve with float center spool, whereby hydraulic fluid pressure difference between said first and second motor fluid ports is controlled; and c) hydraulic valve adjustment. |
12. | The driveline of claim 11 further comprising an automatic traction control unit providing external control signals to said traction control torque generator, said control unit comprising: a) first and second pressure transducers connected to measure pressure in said first and second motor fluid ports of said hydrau lie motor of said traction control torque generator and to communicate said measure¬ ments; b) data measurement: means whereby vehicle performance parameters are measured and transmitted; and c) data processing means, for receiving trans¬ mitted data, computing the required correc tion in pressure difference between said first and second motor fluid ports of said hydraulic motor of said traction control torque generator, and transmitting said 5 difference to each hydraulic valve adjust¬ ment means of said traction control torque generator. |
13. | The driveline of claim 11 further comprising spin 1.0 control brake means adapted for acting variably on said coupling gear means. |
14. | A driveline for a vehicle having a power source, and n driving wheels where n is an integer greater than 2,. |
15. | said driveline comprising a differential of the type described in claim 1 associated with each of said driving wheels, and n 2 bevel gear balancing differ¬ entials whereby said coupling means of respective ones of said differentials are connected by n coupling gear 20 means and said balancing differentials are connected by n 3 coupling gear means. |
16. | 15 The driveline of claim 14 further comprising spin control brake means adapted for.acting variably on 25 said differential case of said differentials. |
17. | The driveline of claim 14, further comprising a traction control torque generator, said traction control torque generator comprising: 30 a) a bidirectional hydraulic motor having an output shaft and a first and second motor fluid port; b) a fourway hydraulic valve with float center spool, whereby hydraulic fluid pressure differ¬ ence between said first and second motor fluid 35 ports is controlled; and c) hydraulic valve adjustment. |
18. | The driveline of claim 16 further comprising an automatic traction control unit providing external control signals to said traction control torque generator, said control unit comprising: a) first and second pressure transducers connected to measure pressure in said first and second motor fluid ports of said hydraulic motor of said traction control torque generator and to communi¬ cate said measurements; b) data measurement means whereby vehicle perform¬ ance parameters are measured and transmitted; and c) data processing means, for receiving transmitted data, computing the required correction in pressure difference between said first and second motor fluid ports of said hydraulic motor of said traction control torque generator, and transmit¬ ting said difference to each hydraulic valve adjustment means of said traction control torque generator. |
19. | An apparatus for transferring power between a power source and a first and second group of driving wheels, comprising: a) an input shaft rotationally connected to said power source; b) a first output shaft for driving connection to said first group of driving wheels; c) a second output shaft; d) a first and a second differential as described in claim 1 having a common differential input shaft and wherein said output shaft of said first differential is rotationally connected to said first output shaft; e) first clutch means whereby said input shaft may be rotationally engaged to either said second input shaft or to said common differential input shaft; f) second clutch means whereby said output shaft of said second differential may be rotationally engaged to said second output shaft; and g) change gear means rotationally connecting said coupling means of said first differential with said coupling means of said second differential. |
Field of the Invention
TECHNICAL FIELD
This invention refers to a driveline of the balanced reaction type for vehicles with two or more driving wheels.
Background of the Invention
BACKGROUND
The greatest force which a vehicle wheel can exert parallel to the surface over which it moves depends on the nature of the wheel and of the surface, commonly expressed as a coefficient of friction, and on the force exerted by the wheel in the direction normal to the surface. Dis¬ tribution of tractive force among driving wheels so as to equalize, to the extent possible, the required coefficient of friction, improves vehicle safety. Performance of vehicles which carry loads of different weight is improved by means which allow adjustment of relative wheel traction in approximate proportion to static wheel loading. Performance of vehicles required to ma¬ noeuvre rapidly is improved by automatic control of rela- tive wheel traction.
PRIOR ART
The bevel gear differential is widely used to sensibly equalize torque transfer to pairs of driving wheels, to pairs of driving axles, and so on, in constructing vehicles with numbers of driving wheels in the sequence 2 , 4, 8,... This has two or more radial arms fixed within a rotatable differential gear case, coaxial with an axle and driven through a differential driving gear, attached to the case, by a driving pinion gear. Bevel gear pinions, one on each radial arm, engage both of two face gears whose axes coincide with that of the axle, located on opposite sides of the radial arms. Each face gear is attached to one half-axle. The bevel gear pinions begin to rotate on the
radial arms whenever the difference in torque transmitted to or from the face gears overcomes static friction, thereby allowing the half-axles to rotate at different rates. Modifications of the bevel gear differential, known as limited slip differentials, locking differentials, etc., are used to limit relative half-axle rotation rate when a reduction in friction coefficient or in normal force allows the corresponding driving wheel to spin. These differen- tials respond automatically to differences in half-axle torque, in rotation rate, or both, to slow one half-axle and so to maintain some torque on the other. These produce sudden changes in relative rotation rate.
US 3,021,725, A.J.R. Schneider, discloses a balanced torque right angle drive applied to a steerable boat propeller. The propeller shaft, with axis at right angles to the drive shaft, is driven through a pair of bevel gears and the resulting reaction torque acts on the propeller shaft housing. On the drive shaft axis, the sun gear of a planetary speed reducer, in the driveline, drives an internal gear through planet gears with axes fixed to a rotatable planet carrier. The reaction torque tending to rotate the planet carrier is utilized to counterbalance that tending to rotate the propeller shaft housing. US 3,053,404, Beck et al, discloses a four wheel drive mine shuttle car with two wheels on either side driven from a locking differential through longitudinal shafts. These locking differentials are driven by transverse shafts from the face gears of a multiplying traction differential, a modification of the bevel gear differential which intermit¬ tently applies a torque to the non-spinning half-axle equal to some multiple of the torque transmitted to the spinning half-axle.
US 3,343,620, A.N. Karavias, discloses a driveline for vehicles with two or more driving wheels. Each wheel is driven from one face gear of a separate bevel gear differ¬ ential, the remaining face gear and differential driving
gear of which are each rotationally connected to either, an adjacent differential or, to the power source. Gears of two differentials are directly connected to the power source so the connections form a closed loop. Equal sized wheels exert sensibly equal tractive force regardless of rotation rates.
US 4,572,318, J.B. Cady, discloses a driveline for four wheeled vehicles with bevel gear differentials in the front and rear axles. The motor drives the planet carrier of a planetary system; the front differential is driven from the sun gear and the rear differential from the annular gear through a standard gear box. This gives ratios of front to rear axle torque from 1:3 to 3:2, without regard to acceleration, as the gear.box is shifted from first to top gear.
US 4,709,775, atanabe et al, disclose a torque control system for four wheel drive vehicles with one bevel gear differential in the front axle and one in the rear. In one embodiment, transmission output torque is carried to each differential through separate, hydraulically actuated, wet disc clutches. In another embodiment, the rear differ¬ ential is driven directly from the transmission while an hydraulically actuated wet disc clutches is used to vary torque acting on the front differential. In both embodi- ments the ratio of torque on front and rear axles is maintained by varying clutch slip under control of a computer programmed according to a mathematical model employing vehicle speed, steering angle, and the difference in axle speed as measured at the differential driving pinion gears. The torque ratio may be fixed or varied according to operating conditions. The mathematical model ensures that maximum torque is applied to the rear wheels at high speeds and small steering angles in order to reduce energy loss due to clutch friction. Colbourne, J.R., "The Geometric Design of Internal Gear Pairs", AGMA, 87, FTM 2, shows that the difference in number of teeth between an internal gear and the cooper-
ating external gear may be as small as five so long as it is possible to assemble the gears axially.
Summary of the Invention The object is to provide a driveline for vehicles with two or more driving wheels by which relative wheel traction can be controlled with lower expenditure of energy than required by systems of the prior art.
This invention therefore provides, 1. differentials, in the form of reduction gearing, through which rotary motion is carried and whose reactive torque is held in balance by,
2. a traction balance, which connects reactive members of the differentials through which rotary motion is carried to or from individual wheels, or groups of wheels, and whose balance may be altered by,
3. traction control change gears, changeable manually, and/or by,
4. traction control torque generators, which apply torque to specific traction balance components in response to external signals, and,
5. spin control brakes by which differential output shafts may be constrained to rotate at a rate propor¬ tional to that of their input shafts. The preferred embodiment of a differential comprises, a differential gear case, rotatably supported through, differential support bearings by the vehicle frame; a differential input shaft, coaxial with the differential support bearings; a first external gear, coaxial with and rotationally connected to the differential input shaft, supported by the differential case through, first external gear support bearings and in mesh with, a first internal gear with axis parallel to that of the differential input shaft and supported by the differential case through, parallel shaft bearings, coaxial with and rotationally connected to, a second external gear, supported by the differential case through the parallel shaft bearings and
in mesh with, a second internal gear, coaxial with the differential input shaft and supported by the differential case through, second internal gear support bearings and rotationally connected to, a differential output shaft coaxial with the differential input shaft; a differential balance gear, coaxial with the differential support bear¬ ings and rotationally connected to the differential case.
When the differential input shaft turns at NT revol¬ utions per unit time, the output shaft at NO, and the differential case at NC, all of positive sign when similar¬ ly directed,
NT - ANO + ' (A - 1)NC = 0 ...(1) where A is the differential speed reduction ratio defined as the ratio, input shaft rotation rate divided by output shaft rotation rate when the differential case is held fixed. When ' torque TT, in units of force times distance, is applied to the input shaft, torque TC to the differenr- tial balance gear, and the differential output shaft applies torque TO to any resisting device, and all are of positive sign when directed parallel to the rotation rate vectors, then, excepting inertial and frictional effects,
TO = TT + TC, ... (2a)
TT = TO/A , ... (2b) and
TC » (A - 1)TT. ... (2c)
When the input shaft is rotated at rate NT regardless of input torque TT, the output torque TO may be controlled by varying TC, or, the output shaft rotation rate NO may be controlled by varying NC. Compact differentials of this type, with A close to but greater than unity, are made using a small difference in number of teeth on internal and cooperating external gears. A traction balance counterbalances the reaction torque acting through the balance gears of n, where n > 1, differ-
entials who input shafts are driven from a single power source at proportional rates and whose output shafts are rotationally connected to driving wheels, while allowing relative rotation of the balance gears, and comprises an assembly of n - 2 bevel gear balancing differentials and 2n - 3 connecting gear trains; when n = 2, the gear train is a rotational connection between the two differential balance gears; when n > 2, n of the connecting gear trains are rotational connections between the balance gear of a differential and either of, one face gear, or, the differ¬ ential driving gear of, a bevel gear balance differential; the remaining face gears and bevel gear differential driving gears are rotationally connected by the n - 3 gear trains remaining, each of which has such number of gears of such relative diameter that reaction torque acting through the differential balance gears, is counterbalanced.
When torque is applied to traction balance components only through differential balance gears, the relationship between the rotation rate of balance gears, NC } , and the relative torque exerted by differential balance gears on the traction balance, r., is
where τ. = TC./TC, • (4) l l 1
By applying equation (1) in the form
(5)
Nτ i " λ i NO i. + (λ i " 1)NC i = ° * equation (3) gives,
∑[τ. λ ./(λ. - 1)]N0 = Cτ j Cλ - 1)]NT. . ...(6)
1 - - ~ i
Equation (6) defines differential action among n wheels. When n = 4, τ- = L,l,b,b, λ. = λ, and NT. = NT, equation (6) becomes, 1 1 1
NO + NO + b(N0^ « NOJ = -2(l.+b)NT/λ • • • • C 7 )
Changing the speed ratio of any gear train within the traction balance changes relative r { values which, according to equations (2) , changes relative differential output shaft torque TO. and so changes relative wheel traction. A traction control torque generator applies torque to one or more rotatable components of the traction balance without regard to component rotation rate, in response to external signals, thereby changing relative r } values. A traction control torque generator comprises, a bi-direc- tional hydraulic motor with, an output shaft for rotatable connection to a traction balance component and with a first and a second motor fluid port through which pressurized hydraulic fluid is supplied to, and evacuated from, the motor fluid ports; a four-way hydraulic valve with float centre spool, which controls pressure difference within, by controlling fluid flow to, and from, motor fluid ports; and, hydraulic valve control means, by which the position of the float centre spool is varied to control traction control torque generation. Bevel gear control differen- . tials and control gear trains may be used to distribute torque from one traction control torque generator to two or more rotatable traction balance components. A first traction control torque generator may be used to alter relative traction with respect to longitudinal wheel position and a second to alter relative traction with respect to transverse wheel position.
Vehicles with all driving wheels disposed in a stra¬ ight line at right angles to their direction of motion may be steered by control torque applied to one rotatable component of the traction balance, by a manually controlled traction control torque generator, so as to increase wheel traction on one side of the centreline while decreasing that exerted by wheels on the opposite side.
A spin control brake acts to slow or stop rotation of a differential case and comprises, a friction brake, which may be rotationally connected directly to the differential case or to a rotatable component of the cooperating trac-
tion balance gear train which is directly connected to the differential case. Spin control brakes may be actuated manually, by external signal, or by centrifugal governor. Full actuation of a spin control brake forces the corre- sponding wheel to rotate at NT/A revolutions per unit time.
Brief Description of the Drawings
Specific embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings in which:
Fig. 1 is a cross-section taken along the axis of a differential according to the invention;
Fig. 2,3 and 4 illustrate schematically the invention applied to a vehicle driveline (Fig. 3 joining Fig. 2 and 4 along lines I-I and II-II) , Fig. 2 showing the front wheel drive. Fig. 3 the transfer unit carrying power between the motor and two groups of wheels, and Fig. 4 showing the driveline for a dual axle rear wheel group;
Fig. 5 is a schematic representation of a triple axle rear wheel group incorporating the differential of the invention;
Fig. 6 is a schematic representation of a vehicle driveline with six driving wheels in parallel steered by a traction control torque generator; Fig. 7 is a schematic representation of a vehicle driveline with two driving wheels in parallel incorporating traction control;
Fig. 8 is a schematic representation of a vehicle driveline with three driving wheels incorporating longi- tudinal and transverse traction control; and
Fig. 9 is a schematic representation of a vehicle driveline with four driving wheels incorporating longitudi¬ nal and transverse traction control.
These drawings illustrate operation of component parts and the manner of making the invention, and merely by way of example, application to specific vehicle types.
In the differential shown by Fig. 1, the differential case consists of differential tube 2, end hubs 4 and 6, and screws 8. The differential case is rotatable in differen¬ tial support bearings 10 and 12, whose outer races are fixed relative to vehicle frame 14 and are held in position by lock washers 16 and 20 and lock nuts 18 and 22, respect¬ ively. Differential input shaft 24, with axis coincident with that of differential tube 2, is connected through spline 26 to first external gear 28, rotatable about the differential tube axis in first external gear support bearings 30 and 32 whose outer races are fixed relative to end hub 6, and are held in position by lock washers 34 and lock nut 36. First internal gear 38, in mesh with first external gear 28, is supported on an axis parallel to that of differential tube 2, through parallel shaft bearings 40 and 42 whose outer races are supported within differential tube 2. Second external gear 44, coaxial with first internal gear 38 and supported through parallel shaft bearings 40 and 42, is rotationally connected to first internal gear 38 by spline 46 and held in alignment by mating surfaces 48 on first internal gear 38 and on second external gear 44. Lock washer 50 and lock nut 52 hold 38 and 44 in position. Second internal gear 54, which meshes with second external gear 44, is rotatable about the axis of differential tube 2 in second internal gear bearings 56 and 58, whose outer races are fixed relative to end hub 4 is held in position by lock washer 60 and lock nut 62. Differential output shaft 64, coaxial with differential tube 2, is rotationally connected to second internal gear 54 by spline 66. A torque is applied to balance gear 68 to balance the reactive torque generated within the differen¬ tial. The assembled differential is balanced dynamically using well known procedure. Differential speed reduction ratio close to unity and relatively small differential tube diameter are achieved using a small difference in number of teeth on internal gears and cooperating external gears. Internal gear pairs are known to experience lower Hertzian
stresses and to be more efficient for a given coefficient of friction than are comparable external gear pairs.
Figs. 2 through 5 illustrate application to a trans¬ port vehicle for off-road use. Fig. 2 shows the driveline of a single axle front wheel group, Fig. 3 shows the transfer unit. Fig. 4 a dual axle rear wheel group, and Fig. 5, an alternative, triple axle rear wheel group. In Fig. 2 main drive shaft 70 carries power between the power source and the transfer unit of Fig. 3. Power is carried between the transfer unit and the front wheels through shaft 72 when the transfer unit is operated in all wheel drive mode. Gears 74 and 76 connect shaft 72 with differ¬ entials 78 and 80 of the type shown in Fig. 1. The output shaft of differential 78 is rotationally connected, via shafts 82 and 84, gears 86 and 88, and left front drive shaft 90, to wheel 92. The output shaft of differential 80 is rotationally connected, via shafts 94 and 96, gears 98 and 100, and right front drive shaft 102, to wheel 104. Reaction torque from the differentials is counterbalanced by the front wheel group traction balance consisting only of gear train 106. Spin control brake 108, a friction brake rotationally connected to the differential case of differential 80, is used to control wheel spin at low speeds. The transfer unit of Fig. 3 may be operated in all wheel drive mode, in which traction ratio of front to rear wheel groups is determined by change gear setting, or, in rear wheel drive mode. Splined shaft 110 is a rotational connection between shaft 70 and clutch slider 112. In all wheel drive mode, clutch slider 112 engages internal spline 114 attached to gear 116 which meshes with gear 118 and is rotationally connected to shaft 120 which forms the input shaft to both front wheel group, differential 122 and rear wheel group differential 124. Shaft 72, the output shaft of front wheel group differential 122, carries power to, or from, the front wheel group. The output shaft of rear wheel group differential 124 carries power to, or from, the
rear wheel group through gear 126 in mesh with gear 128 and attached internal spline 130, to clutch slider 132 and splined shaft 134, and hence to the rear wheel group through rear drive shaft 136. The transfer unit traction balance, consisting of components 138 through 164, counter¬ balances reaction torque acting through the balance gears 138a and 144b of group differentials 122 and 124, respect¬ ively. Splined shaft 140 is rotationally connected to balance gear 138a of front wheel group differential 122 through gear 138b; shaft 142 is rotationally connected to balance gear 144b of rear wheel differential 124 through gear 144a. Shafts 140 and 142 are rotationally connected at any time by one of gear sub-trains 146, 148, or 150. Clutch slider 152 engages internal spline 154, attached to gear 146a, to connect shafts 140 and 142 via gear sub- train 146; clutch slider 156 engages internal spline 158, attached to gear 148a, to connect shafts 140 and 142 via gear sub-train 148, or, clutch slider 156 engages internal spline 160, attached to gear 150a, to connect shafts 140 and 142 via gear sub-train 150. Clutch forks 162 and 164 controls engagement of clutch sliders 154 and 156; a mechanical interlock, not shown, prevents simultaneous engagement. In rear wheel drive, clutch slider 112 engages internal spline 168, rotationally connected to splined shaft 134, while double clutch fork 166 ensures disengage¬ ment of clutch slider 132 from internal spline 130 so rear drive shaft 136 turns at the same rate as shaft 70. Transfer unit spin control brake 170 may be actuated when all wheels of either group tend to spin. (Shaft 136 could also be connected to a standard rear wheel differential.) In the dual axle group shown by Fig. 4, components 172 through 200a of the forward axle are identical with compo¬ nents 206 through 234a of the Rearward axle. Rear drive shaft 136 carries power to, or from, the group, and is rotationally connected to shaft 172 which is rotationally connected to the input shafts of differentials 178 and 180 through hypoid gear pair 174 and 176. The output shaft of
differential 178 is rotationally connected to dual wheel 186 through final reduction gears 182 and 184. The output shaft of differential 180 is rotationally connected to dual wheel 192 through final reduction gears 188 and 190. The dual axle traction balance consists of components 194a through 202 and 228a through 236. Balance gears 194a and 196a of differentials 178 and 180 mesh with gears 194b and 196b, respectively, which are rotationally connected to the first and second face gears, respectively, of bevel gear balancing differential 198. Bevel gear balancing differen¬ tial 198 acts to equalize and add the reaction torque associated with power transfer through differentials 178 and 180, and to apply this to shaft 202 through bevel gear 200a, which is rotationally connected to the differential case of 198, and bevel gear 200b, rotationally connected to shaft 202. Secondary rear drive shaft 204 is a rotational connection between rear drive shaft 136 and shaft 206 through shaft 172. Operation of components 206 through 234b is similar to that of components 172 through 200b, except that shafts 202 and 236 tend to turn in opposite directions when torque is applied through rear drive shaft 136 and resisted by traction. Shaft 238 connects shafts 202 and 236, counterbalancing reaction torque of the two axles. Spin control brakes 240 to 246 inclusive, are actuated manually to control spin within the wheel group.
The triple axle rear wheel group shown by Fig. 5 is an alternative to the dual axle group capable of carrying heavier loads. Rear drive shaft 136 carries power to, or from, the wheel group and is rotationally connected to the forward axle through shaft 248 and hypoid gears 250 and 252, to the centre axle through shaft 248, secondary rear drive shaft 280, shaft 282, and hypoid gears 284 and 286, and to the rear axle through shafts 248, secondary rear drive shaft 280, shaft 282, tertiary rear drive shaft 312, shaft 314, and hypoid gears 316 and 318. The triple axle traction balance consists of components 270a through 278, 304a through 310b and 336a through 354. The case of centre
axle bevel gear balancing differential 308 is rotationally connected to the first face gear of bevel gear balancing differential 348 through bevel gears 310a and 310b. The rear axle bevel gear balancing differential 340 is rota- tionally connected to the second face gear of bevel gear, balancing differential 348 through bevel gears 342a and 342b, shaft 344, and first interaxle balance shaft 346. The forward rear axle bevel gear balancing differential 274 is rotationally connected to the differential case of bevel gear balancing differential 348 through bevel gears 276a and 276b, shaft 278, second interaxle balance shaft 350, shaft 352, and gears 354a through 354c. When driving torque is applied through rear drive shaft 136 and resisted by traction, the two face gears of bevel gear balancing differential 348 tend to turn in the same direction while reaction torque from the forward axle bevel gear balancing differential 274 tends to rotate gear 354c in the opposite direction. When bevel gear pairs 276, 310, and 342 are identical, pinion gears of bevel gear differential 348 exert a torque on the differential case of 348 which is equal and opposite to that exerted by gear 354c, provided the pitch circle diameter of gear 354a is one-half that of gear 354c. Spin control brakes 356 to 366 inclusive are actuated to control spin of wheels within the group. One skilled in the mechanical arts will observe that the wheels of each group may have different diameter, that the final reduction gears may be omitted and speed reduc¬ tion made within the differentials where ground clearance is less critical, and that similarity of components gives some economy. The transfer unit may be used with front or rear axles driven through bevel gear differentials.
Fig. 6 shows the driveline of a vehicle with all driving wheels in parallel in which traction control is used to steer. Main drive shaft 368 carries power to, or from, transverse drive shaft 374 through gears 370 and 372. Differentials 376, with axes coincident with that of the transverse drive shaft carry power between transverse drive
shaft 374 and driving wheels 388 through gears 378, 380, shafts 382, and gears 384 and 386, respectively. The traction balance consists of components 398a through 418f. Opposing face gears of bevel gear balancing differential 390 are rotationally connected the differential cases of differentials 376a and 376b by gear trains 398 and 400, respectively. Opposing face gears of bevel gear balancing differential 392 are rotationally connected to the differ¬ ential case of differential 376c through gear train 402, and to the differential case of bevel gear balancing differential 390 by gear train 414. Opposing face gears of bevel gear balancing differential 396 are rotationally connected to the differential case of differentials 376e and 376f by gear trains 410 and 412, respectively. Oppos- ing face gears of bevel gear balancing differential 394 are rotationally connected to the differential case of differ¬ ential 376d through gear train 408 and to the differential case of bevel gear balancing differential 396 by gear train 416. The differential cases of bevel gear balancing differentials 392 and 394 are rotationally connected by gear train 418. The speed ratio and number of gears in traction balance gear trains 398 to 418 are selected so as to counterbalance torque exerted on the traction balance through the balance gears of the differentials 376 when driving wheels 388 each exert a pre-determined tractive force in response to torque applied through main drive shaft 368. The traction control torque generator 422 consists of a bi-directional hydraulic motor to which hydraulic fluid under pressure is provided and evacuated through the two motor fluid ports under control of a four- way hydraulic valve with float centre spool which is manually controlled when steering. This allows differen¬ tial action between all wheels except when the valve spool is at either end of its stroke. Spin control brakes 424 are used to control wheel spin at low speeds. The braking torque at which spin control brakes slip should be less
than that which would damage the driveline if all but one wheel encounter negligible resistance to traction.
Fig. 7 shows the driveline of a vehicle with two driving wheels in parallel. Main drive shaft 426 acts through shaft 428 and gears 430 and 432 to carry power to, or from, the common input shaft of differentials 434 and 436. The output shafts of differentials 434 and 436 are rotationally connected to wheels 438 and 440, respectively. The traction balance consists of components 442, through which reaction torque of the two differentials is counter¬ balanced. When traction control torque generator 444 applies torque to the traction balance, the reaction torque and according to equations (2) , the output torque, of one differential is- reduced while thoseof the other are corre- spondingly increased. The traction control torque gener¬ ator may be controlled manually or by an automatic control unit which includes a pressure transducer to measure pressure in each motor fluid port of the traction balance hydraulic motor, data measurement means and data processing means. Measurements of vehicle performance data such as transverse acceleration, steering angle and its rate of change, transmission output torque, etc. , are processed by a data processing unit programmed according to a mathemat¬ ical model appropriate to the vehicle and its service requirements. The data processing unit repeatedly computes optimum traction distribution and from this the required pressure difference between motor fluid ports of the hydraulic motor in the traction balance torque generator. The difference between optimum pressure difference is used to continuously correct the spool position of the hydraulic valve. Actuation of spin control brake 446 slows or stops rotation of the differential cases and so forces the wheel rotation rates toward the average.
Fig. 8 shows the invention applied to the driveline of a vehicle with three driving wheels. Main drive shaft 448 acts through gears 450, 452, and 454 to carry power to, and from, differentials 456, 458, and 460. The output shafts
of differentials 456, 458, and 460 are rotationally con¬ nected to wheels 468, 478, and 486, respectively through gears 462 and 464, 470 and 472, and 480 and 482, and shafts 466, 474 and 484, respectively. The traction balance consists of components 488a to 494 inclusive. Gear trains 488 and 490 are rotational connections between the differ¬ ential case of differentials 456 and 458, and the first and the second face gears, respectively, of bevel gear balanc¬ ing differential 494. Gear train 492 is a rotational connection between the differential case of differential 460 and the differential case of bevel gear balancing differential 494. The speed ratios of gear trains 488, 490, and 492 are made so bevel gear balancing differential 494 counterbalances reaction torque from differentials 456, 458, and 460 when traction forces are in the ratio required for normal operation. The transverse traction control torque generator 496, applies control torque to the trac¬ tion balance through gear 488b. When negligible wheel slip occurs, a torque, independent of rotation rate, applied by 496 changes that torque counteracting reaction torque of differential 456, and equations (2) show that both output and input torque of differential 456 must change by corre¬ sponding amounts as must the tractive force applied by wheel 468. The change in input torque to differential 456 from gear 450 then acts with opposite effect on gear 454 and so on the input shafts of differentials 458 and 460, changing output and reaction torque as well as tractive force exerted by wheels 478 and 486. The changed reaction torque of differentials 458 and 460 act through gear trains 490 and 492, bevel gear balancing differential 494, and gear 488c to balance the reactive torque of 456 plus the traction control torque. This changes traction exerted by wheel 468 in one direction and that exerted by wheels 478 and 486 by a corresponding total amount, in the opposite direction. The longitudinal control torque generator acts directly on the case of bevel gear balancing differential 494 to change traction exerted by wheel 486 in one direc-
tion and the total traction on wheels 468 and 478 in the opposite direction. Where vehicle service requires, an automatic traction control unit programmed to continuously adjust the two traction control torque generators is used. Each of spin control brakes 500, 502, and 504, when ap¬ plied, acts to slow or stop rotation of the associated differential case, forcing the corresponding wheel toward a rate of rotation directly proportional to that of main drive shaft 448. The driveline of a vehicle with four driving wheels is shown by Fig. 9. Main drive shaft 506 acts through gears 508, 510, and 512 to carry power to, or from, differentials 514 through 520. Differentials 514 through 520 are rota¬ tionally connected to wheels 528, 536, 544 and 552 through gears 522 and 524, 530 and 532, 538 and 540, and 546 and 548, shafts 526, 534, 542, and 550, respectively. The traction balance consists of components 554a to 566b inclusive. Gear trains 554 and 556 are rotational connec¬ tions between differential cases of differentials 514 and 516, respectively, and the first face gears of bevel gear balancing differentials 558 and 560, respectively. Gear trains 562 and 564 are rotational connections between differential cases of differentials 518 and 520, respect¬ ively, and the second face gears of bevel gear balancing differentials 558 and 560, respectively. Gear train 566 is a rotational connection between the differential cases of bevel gear balancing differentials 558 and 560. The speed ratio of each of the gear trains 554, 556, 562, 564, and 566, is selected so the torque exerted by bevel gear balancing differential 558 on gear 566a counterbalances the torque exerted by bevel gear balancing differential 560 on gear 566b when wheel tractive forces are in the ratio required for normal operation. Transverse traction control torque generator 568 applies control torque to traction balance gear 566a through gear 570, thereby changing traction exerted by wheels 528 and 544 in one direction while changing traction exerted, by wheels 536 and 552 in
the opposite direction. Longitudinal traction control torque generator 572 applies control torque directly to the differential case of bevel gear differential 574, which distributes this to gears 562b and 564b and thereby changes traction exerted by wheels 528 and 536 in one direction while changing that exerted by wheels 544 and 552 in the opposite direction. Where vehicle service requires, an automatic traction control unit, programmed to continuously adjust torque applied by the traction control torque generators, is used. Spin control brakes 580 through 586 operate as described for a driveline with three driving wheels.
Change gears incorporated in gear trains of a traction balance allow adjustment of relative wheel traction only in finite steps and are applicable to vehicles which carry loads of markedly different weights. Traction control torque generators are able to continuously adjust relative wheel traction and have wider application. The technology used in making automatic traction control units is well known. Spin control brakes allow direct operator control at low speed, eliminating the sudden uncontrolled changes in relative wheel traction associated with some drivelines of the prior art.
As will be apparent to those skilled in the art in the light of the foregoing disclosure, many alterations and modifications are possible in the practice of this invention without departing from the spirit or scope thereof. Accordingly, the scope of the invention is to be construed in accordance with the substance defined by the following claims.
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