(12) United States Patent 

US006957731B2 

(10) Patent N0.: US 6,957,731 B2 

Lawson, Jr. (45) Date of Patent: Oct. 25, 2005 

(54) DRIVE SYSTEM FOR STABILITY AND 3,583,508 A * 6/1971 Waddington et al. .... .. 180/6.44 

DIRECTIONAL CONTROL OF VEHICLES 3,698,498 A * 10/1972 Stanford ................... .. 180/6.2 

AND AIRCRAFT 4,300,231 A 11/1981 Mo?itt 

4,745,987 A * 5/1988 Buschmann .............. .. 180/197 

(76) Inventor: Thomas Towles Lawson, Jr., 500 Ct. * 

Square, #1001, Charlottesville, VA (Us) 4,754,824 A * 7/1988 Olsson .................... .. 180/6.48 

22902 4,895,052 A 1/1990 Gleasman et al. ........... .. 475/7 

5,394,764 A 3/1995 Fini, Jr. 

( * ) Notice: Subject to any disclaimer, the term of this 

patent is extended or adjusted under 35 * cited by examiner 

U.S.C. 154(b) by 0 days. 

(21) Appl. N0.: 10/704,024 Primary Examiner—Richard M. Lorence 

(22) Filed NOV 7 2003 (74) Attorney, Agent, or Firm—LaWrence E. Laubscher, Jr. . . , 

(65) Prior Publication Data (57) ABSTRACT 

Us 2004/0116232 A1 Jun- 17, 2004 Adrive assembly for a bilaterally symmetrical machine such 

Related U S Application Data as a vehicle or aircraft is provided to precisely control and 

(60) Provisional application No. 60/425,229, ?led on Nov. 8, Vary engine power delivered to a pair of Opposed drive 

2002, mechanisms of the assembly. Each drive mechanism 

(51) Int C17 F16H 37/06 includes a ?rst differential clutch connected With a poWer 

(52) US. Cl. ..................... .. 192/218' 192/13 R' 192/49' Source Via a power Splitter’ a drive element Such as a Wheel 

, 74/650; ,74/665 F, or propeller connected With the ?rst differential clutch, and 

(58) Field of Search ............................... .. 192/218, 220, a ?rst braking deviee eerlrleeted With the ?rst differential 

192/2221, 13 R, 49; 74/650, 665 F—665 K; clutch to independently control the delivery of poWer to the 

475/221; 180/6-2—6-7 drive element. A second differential clutch may be provided 

_ for each drive mechanism to control movement of the drive 

(56) References Clted mechanism in an opposite direction. 

U.S. PATENT DOCUMENTS 

1,732,405 A 10/1929 InverniZZi 5 Claims, 2 Drawing Sheets 

102 

SOURCE 

POWER / 

120 122 

/ 130 124 

112 

100 

104 114 

126 132 / 

‘ 134 / , 13a 128 ‘Pa / “0/ j 

DRNE - 2ND ' 154 )4 POWER 18f ‘"9 DRIVE 

ELEMENT aw. uFF. SPLITTER D'FF- D'FF' ELEMENT 

k ‘I 129 

136 140 

142 144 

12s 

CONTROLLER 
U.S. Patent Oct. 25,2005 Sheet 1 of2 US 6,957,731 B2 

DRIVE / DRNE 

ELEMENT ELEMENT 

POWER 

SOURCE 

/ POWER / 

SPLITTER 

CONTROLLER 

FIG.1 
U.S. Patent Oct. 25,2005 Sheet 2 of2 US 6,957,731 B2 

5 

3; 

03. 

3 

E5 mwtzmm \ . $261E 

\o: 8? 

2: 

N2 \ 5 x:

m2 8, 

.wE NKBJOMPZOU 

NE. 

NS. 
US 6,957,731 B2 

1 

DRIVE SYSTEM FOR STABILITY AND 

DIRECTIONAL CONTROL OF VEHICLES 

AND AIRCRAFT 

This application claims the bene?t of US. Provisional 

Application No. 60/425,229 ?led on Nov. 8, 2002. 

BACKGROUND OF THE INVENTION 

This invention relates to modern engine driven 

machinery, both land bound and airborne, Which are pro 

pelled and steered by varying the relative speed of tWo or 

more laterally positioned drive mechanisms. 

Differentials are mechanical devices used almost uni 

formly on vehicles Whose driven Wheels have occasion to 

rotate at different speeds. When making a turn, the outside 

Wheel of a vehicle travels in a Wider arc, and therefore must 

rotate faster than the opposing Wheel. Furthermore, a Well 

knoWn method of traction control is to selectively apply the 

brakes of Wheels that slip because of lack of traction. 

Accordingly, a differential can be used to transmit torque 

and horsepoWer by brake actuation. 

In a traditional clutch, a rotating friction surface causes 

another surface to rotate and the friction surface Wears With 

each engagement. Increasing the life or torque capacity of 

the clutch requires adding Weight to the rotating mass. 

The present invention uses a differential clutch arrange 

ment applied to tWo shafts rotating in opposing directions. 

By selectively applying braking action to limit or control the 

rotation of one of the shafts, the alternative shaft transmits 

the engine poWer to the drive mechanisms. 

BRIEF DESCRIPTION OF THE PRIOR ART 

Rotors of an aircraft employing line vorteX generating 

rotors are described in US. Pat. No. 5,954,295 to Olson. 

Such rotors Would never need reverse, so only one differ 

ential is needed per side. If both brakes are fully activated, 

then both rotors rotate at the same speed. Roll of the aircraft 

is accomplished by reducing pressure on the brake of the 

rotor on the side of the desired roll direction, until the 

reduction of the rotor speed accomplishes the roll. Fine and 

positive control of the rotor speed provides good control of 

the aircraft. Multiple engines can be linked for redundancy 

of the drive unit. HoWever, the Olson machine cannot ?y if 

one rotor loses poWer. 

Traction for many types of agricultural and construction 

equipment is provided by parallel tracks or belts. Steering is 

accomplished by varying the speed of the tracks relative to 

one another. Three techniques are used to achieve speed 

variation. The oldest technique utiliZes clutches and brakes. 

Disengaging a track from the engine by applying the brake 

to that track, While alloWing the other track to continue 

moving at the same speed, turns the vehicle. It should be 

noted that merely putting a differential betWeen the tracks 

and applying the brake to one track Will double the speed of 

the other track. The combined resistance of the locked track 

and the force needed to accelerate the machine around its 

vertical aXis Would require too much poWer. 

Atechnique Which has become more common recently is 

the use of a dual path hydrostatic system. TWo variable 

displacement pumps drive hydraulic track motors in either 

forWard or reverse directions. The popularity of the hydro 

static system is based on three characteristics. One charac 

teristic is the in?nitely variable gear ratios derived from the 

different amounts of ?uid being pumped. A second charac 

teristic is the ability of the tracks to rotate in opposite 

10 

15 

20 

25 

30 

35 

40 

45 

50 

55 

60 

65 

2 

directions, and the third is modularity, because the pumps 

and motors need only be connected by hoses. Some draW 

backs to this system are the entropies of heat and friction by 

pumping losses and the high eXpense of the variable dis 

placement pumps. 

To compete With the dual path hydrostatic transmission, a third technique of direction control has been developed. This 

third system uses tWo differentials, one for each track, and 

therefore does not suffer the pumping losses of the hydro 

static technique, at least not in straight-ahead travel. Each 

track has its oWn differential Where one side of the differ 

ential is attached to the track, the second side is driven, and 

the third side is geared to a hydraulic motor. The driven side 

of both differentials turns at the same speed, so the speed of 

the hydraulic motor determines the relative speed of the 

tracks. The speed of the steering motor is still controlled by 

a variable displacement pump, but it can be smaller than the 

pumps required for the hydrostatic method, and only one 

pump is needed. 

Accordingly, there is a need for an improved drive system 

that eliminates the high cost and maintenance issues asso 

ciated With dual path hydrostatic systems. 

SUMMARY OF THE INVENTION 

The present invention alloWs in?nitely controllable 

motion and steering control for a machine having a bilater 

ally symmetrical drive system poWered by a poWer source. 

A differential clutch and brake are employed to vary the 

poWer supplied to the drive element of each half of the drive 

system. Equal poWer applied to each output shaft results in 

straight line travel, Whereas providing unequal poWer to 

each output shaft results in a turn by the machine. 

In another embodiment, each drive mechanism has tWo 

differential clutches and braking devices associated With the 

drive half rather than the single differential clutch and brake 

of the ?rst embodiment. A pair of differential drive shafts 

eXtend betWeen the differentials, each rotating in opposite 

directions. The addition of the second differential alloWs 

forWard and reverse motion of travel. Counter-rotation is 

accomplished by engaging the brake of the forWardly rotat 

ing differential drive shaft on one side of the machine While 

simultaneously engaging the reversely rotating differential 

drive shaft on the opposite side of the machine. 

BRIEF DESCRIPTION OF THE DRAWINGS 

Other advantages of the invention Will become apparent 

from a study of the folloWing speci?cation When vieWed in 

light of the accompanying draWing, in Which: 

FIG. 1 is a schematic diagram of a ?rst embodiment of the 

differential drive and stability system for movement in one 

direction; and 

FIG. 2 is a schematic diagram of a second embodiment of 

the differential drive and stability system Where movement 

in forWard and reverse directions is required. 

DESCRIPTION OF THE PREFERRED 

EMBODIMENT 

Referring to FIG. 1, a differential clutch drive system for 

bilaterally symmetrical machines Where reverse operation is 

not required according to a ?rst embodiment of the invention 

Will be described. 

ApoWer source 2 is connected With a poWer splitter 4 via 

a drive shaft 6. The splitter includes output shafts 8 and 10, 

Which are connected With differential clutches 12 and 14, 

respectively. Because the splitter delivers the same output to 

the differential clutches, the drive system is bilaterally 

symmetrical. 
US 6,957,731 B2 

3 

Each differential clutch has an output drive shaft 16, 18 

connected With a driven element 20, 22. The driven element 

could be a Wheel, a track, a propeller, or the like. The 

operation of each differential clutch is individually con 

trolled by a braking device 24, 26. The braking device may 

be of any conventional type, including disk or drum friction 

brakes, oil or air pumps, or an electric motor. 

Negative torque or braking action from a braking device 

engages the differential clutch With Which it is connected to 

turn the output shaft connected With that clutch to drive the 

associated drive element. Because the braking devices are 

independently controlled by the operator via a controller 28, 

the amount of driving force applied to each drive element 

from the poWer source can be controlled to propel and steer 

the vehicle. 

For example, if the driving element 20 is the left drive 

Wheel of a vehicle and the driving element 22 is the right 

drive Wheel of the vehicle, the vehicle Will be propelled in 

a straight line When the drive force applied to each drive 

element is equal. In order to turn the vehicle to the left, the 

operator can increase the braking action of braking element 

26 on the right differential clutch 14, thereby increasing the 

output of the shaft 18 and increasing the driving force to the 

right drive Wheel relative to the left drive Wheel. 

The amount of torque supplied to the driving elements can 

be easily and in?nitely varied by the operator. Thus, all of 

the output from the poWer source can be supplied to either 

differential clutch, or the output can be divided betWeen the 

clutches in any ratio. 

In the drive system of FIG. 1, only driving forces in one 

direction can be obtained. In the embodiment shoWn in FIG. 

2, driving forces in tWo directions are obtained because a 

second differential clutch and braking device are connected 

With each driving element. 

More particularly, FIG. 2 shoWs a driving system includ 

ing a poWer source 102 connected With a poWer splitter 104 

via a drive shaft 106. The poWer splitter includes output 

shafts 108 and 110, Which are connected to the ?rst differ 

ential clutches 112 and 114, respectively. First differentials 

112 and 114 have a single input Which receives poWer from 

the output shafts 108, 110 from the poWer splitter, and tWo 

outputs, Which are connected to second differentials 130, 

132 via their respective output shafts. More particularly, 

output shafts 134 and 136 connect ?rst differential 112 to the 

second differential 130, While output shafts 138 and 140 

connect ?rst differential 114 to second differential 132. 

Output shafts 134, 138 rotate in a ?rst direction, While output 

shafts 136, 140 rotate in the opposite direction. Second 

differentials 130, 132 have tWo inputs and a single output. 

Because the splitter delivers the same output to the differ 

ential clutches, the drive system is bilaterally symmetrical. 

Each second differential clutch has an output drive shaft 

128, 129 connected With a driven element 120, 122. The 

driven element could be a Wheel, a track, a propeller, an 

impeller, or the like. The operation of each differential clutch 

is individually controlled by braking devices 124, 126, 142, 

and 144. As in the embodiment of FIG. 1, the braking 

devices may be of any conventional type. 

Braking action from one of the braking devices sloWs or 

stops the rotation of the corresponding shaft spinning in a 

?rst direction and engages the differential clutch of the ?rst 

differential shaft With Which it is connected, thereby alloW 

ing poWer to be transmitted to the output shaft rotating in the 

10 

15 

25 

35 

40 

45 

55 

4 

opposite direction. The rotating shaft transmits poWer turn 

ing the other output shaft Which is also connected to the 

second differential. Because the braking devices are con 

trolled independently via a controller 128 by the operator, 

the amount of driving force applied to each drive element 

from the poWer source can be controlled to propel the drive 

element in a forWard or reverse direction as Well as to steer 

the vehicle. 

For eXample, if braking elements 124, 126 are engaged, 

poWer from the poWer source is transmitted to second 

differential clutches 130, 132 by output shafts 136 and 140, 

respectively, thereby facilitating reverse motion. If braking 

elements 142, 144 are engaged, poWer from the poWer 

source is transmitted to second differential clutches 130, 132 

by output shafts 134 and 138, respectively, thereby provid 

ing forWard motion. 

If drive element 122 represents a left Wheel, and drive 

element 124 represents a right Wheel, then to execute a right 

turn, braking elements 142, 126 are engaged, thereby caus 

ing poWer from the poWer source to transmit to second 

differential clutches 130, 132 by output shafts 134 and 140, 

respectively, thereby facilitating a Zero-radius turn to the 

right. A Zero-radius left turn is accomplished by engaging 

braking elements 124 and 144. 

While the preferred forms and embodiments of the inven 

tion have been illustrated and described, it Will be apparent 

to those of ordinary skill in the art that various changes and 

modi?cation may be made Without deviating from the 

inventive concepts set forth above. 

What is claimed is: 

1. Adrive assembly for a bilaterally symmetrical machine, 

comprising: 

(a) a poWer source; 

(b) a poWer splitter connected With said poWer source; and 

(c) a pair of opposed drive mechanisms connected With 

said poWer splitter, each drive mechanism including: 

(1) a ?rst differential clutch connected With said poWer 

splitter and a second differential clutch connected 

With said ?rst differential clutch; 

(2) a drive clement connected With said second differ 

ential clutch; 

(3) ?rst and second braking devices connected betWeen 

said ?rst and second differential clutches to control 

the delivery of poWer from said poWer splitter to said 

drive element, Whereby operation of said ?rst and 

second braking devices controls the degree and 

direction of driving poWer being delivered from said 

poWer source to said driving elements. 

2. A drive assembly as de?ned in claim 1, and further 

comprising a controller connected With said ?rst and second 

braking devices. 

3. A drive assembly as de?ned in claim 2, Wherein said 

driving element comprises one of a Wheel, a track, a 

propeller, and an impeller. 

4. A drive assembly as de?ned in claim 2, Wherein said 

braking device comprises one of a disk and drum friction 

brake, a motor, and a pump. 

5. A drive assembly as de?ned in claim 2, Wherein each 

of said drive mechanisms includes a ?rst drive shaft con 

necting ?rst differential clutch With said poWer splitter and 

a pair of second drive shafts arranged betWeen said ?rst and 

second differential clutches.