# (12) United States Patent US006957731B2 

## (10) Patent N0.: US 6,957,731 B2 Lawson, Jr. (45) Date ofPatent: Oct. 25, 2005

(54) DRIVE SYSTEM FOR STABILITYAND 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 ANDAIRCRAFT 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 anydisclaimer, the term ofthis patent is extended or adjusted under 35 * cited by examiner 

### U.S.C. 154(b) by 0 days.
(21) Appl. N0.: 10/704,024 PrimaryExaminer—Richard M. Lorence (22) Filed NOV 7 2003 (74) Attorney,Agent, orFirm—LaWrence E. Laubscher, Jr.

. . , 

### (65) Prior Publication Data (57) ABSTRACT

Us 2004/0116232A1 Jun- 17, 2004 Adrive assemblyforabilaterally symmetricalmachine 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, orpropeller connectedWith 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 ofpoWer to the 

### 475/221; 180/6-2—6-7 drive element.Asecond differential clutchmaybeprovided

_ 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 

# POWER / SOURCE 

### 120 122 

# / 124 100 126 132 / 130 112 104 114 

## ‘ 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



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## US 6,957,731 B2 1
DRIVE SYSTEM FOR STABILITYAND DIRECTIONAL CONTROL OF VEHICLES ANDAIRCRAFT


### 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 avehicle travels in aWider arc, and therefore must rotate faster than the opposing Wheel. Furthermore, a Well 

### knoWnmethod oftraction 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. 

### Byselectivelyapplyingbrakingactionto limitorcontrolthe 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. Ifboth brakes are fully activated, thenboth rotors rotate at the same speed. Roll ofthe aircraft 

### is accomplished by reducing pressure on the brake of the rotor on the side of the desired roll direction, until the 

### reduction ofthe rotor speed accomplishes the roll. Fine and 

### positive control ofthe rotor speedprovides good control of the aircraft. Multiple engines can be linked for redundancy ofthe drive unit. HoWever, the Olson machine cannot ?y if

one rotor loses poWer.



### Traction for many types of agricultural and construction 

### equipmentisprovidedbyparalleltracksorbelts. Steeringis accomplishedbyvarying the speed of the tracks relative to
one another. Three techniques are used to achieve speed 

### variation. The oldest technique utiliZes clutches andbrakes. 

### 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 thebrake to one trackWill 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 Whichhas 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?nitelyvariable gear ratiosderived from the 

### different amounts of ?uid being pumped. Asecond charac teristic is the ability of the tracks to rotate in opposite 10

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## 2 directions, and the third is modularity, because the pumps and motors need only be connected by hoses. Some draW backsto this system are the entropies ofheat and frictionby 

### pumping losses and the high eXpense of the variable dis 

### placement pumps.

To competeWith the dualpathhydrostatic transmission, a thirdtechnique ofdirectioncontrolhasbeendeveloped.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 ahydraulicmotor. The driven side ofboth differentials turns at the same speed, so the speed of 

### the hydraulic motor determines the relative speed of the 

### tracks. The speed ofthe steeringmotor is still controlledby
avariable displacementpump,but it canbe smaller than the 

### pumps required for the hydrostatic method, and only one pump is needed.

Accordingly, there is aneed for an improveddrive 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 systempoWered by apoWer source. A differential clutch and brake are employed to vary the poWer supplied to thedrive elementofeachhalfofthedrive 

### system. EqualpoWer 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 andbrakingdevices associatedWith the drive halfrather than the single differential clutch andbrake of the ?rst embodiment. Apair 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 

### accomplishedby engaging thebrake ofthe forWardly rotat ing differential drive shaft on one side ofthe 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 ofthe folloWing speci?cationWhen vieWed in 

### light of the accompanying draWing, in Which:

FIG. 1 is a schematicdiagram ofa ?rstembodimentofthe differential drive and stability system for movement in one 

### direction; and

FIG. 2 is a schematicdiagram ofa 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 symmetricalmachinesWhere reverse operationis notrequired accordingto a ?rstembodimentofthe invention Will be described.

ApoWer source 2 is connected With apoWer splitter 4via a drive shaft 6. The splitter includes output shafts 8 and 10, Which are connected With differential clutches 12 and 14, respectively. Because the splitterdelivers the same outputto 

### 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 connectedWith 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 

### trolledby abraking device 24, 26. The braking device may be ofany 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 controlledbythe operatorviaa 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 ofbraking element 

### 26 on the right differential clutch 14, thereby increasing the output ofthe shaft 18 and increasing the driving force to the right drive Wheel relative to the left drive Wheel.

The amountoftorque suppliedto thedrivingelementscan 

### 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 canbe 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 apoWer source 102 connectedWith apoWer 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 inputWhich receivespoWer 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 ?rstdifferential 112 to the 

### second differential 130, While output shafts 138 and 140 connect ?rst differential 114 to second differential 132. 

### Outputshafts 134, 138rotate ina?rstdirection,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,orthe like.Theoperationofeachdifferentialclutch 

### is individually controlledbybrakingdevices 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 ingpoWertobetransmittedto the outputshaftrotating inthe 10

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## 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, ifbraking elements 124, 126 are engaged, poWer from the poWer source is transmitted to second 

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

### respectively, thereby facilitating reverse motion. Ifbraking elements 142, 144 are engaged, poWer from the poWer source is transmitted to seconddifferentialclutches 130, 132 

### by output shafts 134 and 138, respectively, therebyprovid ing forWard motion.

If drive element 122 represents a left Wheel, and drive element 124 represents a rightWheel, then to execute aright 

### turn, braking elements 142, 126 are engaged, thereby caus ing poWer from the poWer source to transmit to second 

### differential clutches 130, 132by 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 thepreferred forms andembodiments ofthe inven 

### tion have been illustrated and described, it Willbe apparent to those ofordinary skill in the art thatvarious changes and 

### modi?cation may be made Without deviating from the inventive concepts set forth above.

What is claimed is: 

### 1.Adriveassemblyforabilaterallysymmetricalmachine, 

## comprising:

(a) a poWer source; (b) apoWersplitterconnectedWithsaidpoWersource; and 

### (c) a pair of opposed drive mechanisms connected With



### said poWer splitter, each drive mechanism including: (1) a ?rst differential clutch connectedWith saidpoWer

splitter and a second differential clutch connected 

### With said ?rst differential clutch; (2) a drive clement connected With said second differ



### ential clutch; (3) ?rstand secondbrakingdevicesconnectedbetWeen

said ?rst and second differential clutches to control 

### thedeliveryofpoWer from saidpoWersplitterto said 

### drive element, Whereby operation of said ?rst and second braking devices controls the degree and directionofdrivingpoWerbeingdelivered from said poWer source to said driving elements. 2. A drive assembly as de?ned in claim 1, and further comprising a controller connectedWith 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. Adrive 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
apair ofseconddrive shafts arrangedbetWeen said ?rst and second differential clutches.