A two speed drive system for a wheel of a vehicle by which shifting from one speed to the other is accomplished by the inherent mechanism of the wheel is described. A description of the speed shifting operation is provided and diagrams of the mechanism are included. Possible application to lunar roving vehicles is proposed

Burch, J. L.

English

NASA Technical Reports Server

REPLY TO
ATTN OF: GP
NATIONAL AERONAUTICS AND SPACE ADMINISTRATION
WASHINGTON, D.C. 20546
MAY 3 1 1974
TOs ISI/Scientific & Technical Information Division
Attn: Miss Winnie M. Morgan ~~~
FROM: GP/Office of Assistant General
Counsel for Patent Matters
SUBJECT: Announcement of NASA-Owned U.S. patents in STAR
In accordance with the procedures agreed upon by Code GP
and Code KSI, the attached NASA-owned U.S. Patent is being
forwarded for abstracting and announcement in NASA STAR.
The following information is provided:
U.S. Patent No. :
Government or
Corporate Employee
Supplementary Corporate
t^y source (if applicable)
NASA Patent case No.
G6oe-f/i
NOTE - If this patent covers an invention made by a corporate
employee of a NASA Contractor, the following is applicable;
YES NO
Pursuant to Section 305(a) of the National Aeronautics and
Space Act, the name of the Administrator of NASA appears on
the first page of the patent; however, the name of the actual
inventor (author)—appears-at the-heading of column No. 1 of
the Specification, following the words "...with respect to
an invention of ..."
Bonnie L. Woerner
Enclosure
Lrtt
https://ntrs.nasa.gov/search.jsp?R=19740014957 2020-03-17T14:43:03+00:00Z
United States Patent
Burch
us] 3,678,771
[45) July 25, 1972
[54] TWO-SPEED DRIVE SYSTEM
[72] Inventor: John L. Burch, Decatur, Ala.
[73] Assignee: The United States of America as
represented by the Administrator of the
National Aeronautics and Space Adminis-
tration
(22| Filed: Dec. 31, 1970
[21] Appl. No.: 103,091
[52] U.S. Cl 74/217 R
[51] Int-Cl F16h9/00
[58] Field of Search 74/217 R
[56] References Cited
FOREIGN PATENTS OR APPLICATIONS
855,158 11/1952 Germany 74/217 R
Primary Examiner—C. J. Husur
Attorney—L. D. Wofford, Jr., W. H. Riggins and John R.
Manning
[57] ABSTRACT
A two-speed drive system for driving an independently driven
vehicle wheel comprising a relatively large wheel sprocket at-
tached to the vehicle wheel. A drive belt passes around the
large wheel sprocket and one of a pair of smaller, selectively
interchangeable, motor-driven wheels. The two smaller
wheels are of the same diameter but rotate at different speeds
and are mounted on a plate that may be temporarily released
through a latching pawl for rotation of 180° so that the two
wheels change places. No external force is required to rotate
the plate, when released, since one of the smaller wheels turn-
ing in contact with the drive belt causes the plate to rotate
rather then the drive belt and large wheel sprocket. When the
drive belt is engaging both of the smaller wheels simultane-
ously during the shifting phase, the normally slower turning
wheel is permitted to turn faster through a ratchet mechanism.
8 Claims, 5 Drawing Figures
55
Patented July 25, 1972
3 Sheets-Sheet l
3,678,771
55
FIG. I
JOHN L. BURCH
INVENTOR
BY
ATTORNEY
Patented July 25, 1972 3.678,771
3 Sheets-Sheet 2
63
73
77
39
29
19
FIG. 2
FIG.5
BY
JOHN L BURCH
INVENTOR
ATTORNEY
^ Patented July 25, 1972 3,678,771
3 Sheets-Sheet 3
to
ro
JOHN L. BURCH
INVENTOR
BY
{(•
ATTORNEY
3,678,771
_ , . - 1 2
TWO-SPEED DRIVE SYSTEM BRIEF DESCRIPTION OF THE DRAWING
.ORIGIN OF THE INVENTION FIG. 1 is a pictorial view showing a two-speed drive system
arranged in the low-speed position and installed on the inside
The invention described herein was made by an employee
 of a spoked wheel for driving the wheel.
of the United States Government and may be manufactured FIG. 2 is a schematic elevational view of the two-speed
and used by or for the Government for governmental purposes drive system of FIG. 1 taken generally along line 2—2 of FIG.
without the payment of any royalties thereon or therefor. 1 and showing the drive system in the low-speed position.
„ .^.,^,r^, ,v,~ ~^-™.,-.v,.,.-.m~ FIG. 3 is a view similar to FIG. 2 but showing the driveBACKGROUND OF THE INVENTION ,0 system during the shifting phase from one speed to fhe other
This invention relates generally to drive systems and more nG- 4 « a ™evt similar to FIG. 2 but showing the drive
particularly to a two-speed drive system for a wheel of a vehi- svstem in the high-speed position,
cle wherein the shifting from one drive speed to the other FIG 5 is an en'ar«ed ™w> ?*«>*% «•» section, showing a
drive speed is effected by means inherent in the drive system. ratchet mechamsm operative during the speed shifting phase
Multispeed drive systems known in the prior art vary con- 15 for Permittj"8 *e low-speed power transmitting wheel to turn
siderably in design and thus in reliability, complexity, cost and at a faster than normal speed'
maintenance requirements. Some of the systems utilize a plu- DESCRIPTION OF THE PREFERRED EMBODIMENT
rality of shifting gears that run in a bath of heavy oil or grease
and are associated with clutches and shifting mechanisms that
 20 Referrin8to FIG- l> ^ erem is shown a wheel drive sprocket
result in a rather costly, complex and heavy apparatus that 11 attach?d !° sP°ke? 13 of a driven wheel " which may be
requires considerable maintenance. Certain of the simplified on.e w.hee. of a vehl'le wh.<™n the whe'k °f the vehlclef \re
... . . . . , . . . . . individually dnven through the two-speed dnve system of the
systems, while being less costly and complex, involve the m-
 inv
y
ention Jhe
 8
okes ,3 ^£ from Jhed hub ,
convenience of manually transferring a dnve belt or chain ^
 tums Qn an ^ J and th fe hed h
from one sprocket to another sprocket of different diameter. 25 ^
 f j conventiona, dam £ (Mt vjsible jn {ne draw.
Iii certain dnve system applications it is particularly desira- jj,_\
We that the drive system be very simple, lightweight and relia-
 Welded to the axle 17 is a triangular bracket plate 19 rein-
ble and yet provide a low maintenance system having a con-
 forced by a corner brace 21. The bracket 19 has a pair of ex-
venient means for shifting speeds. Such a drive system appears
 3Q tensions 23, each having an end of a fixed shaft 25 joined
to be applicable, for example, in wheeled vehicles for trans- thereto and on which an idler 27 turns. Each of the shafts 25 is
porting astronauts as they explore the lunar surface. It is an- fixed at the other end to a relatively large stationary plate
ticipated that the wheels of these lunar vehicles will be in- member 29. A rotatable circular plate member 33 is pivotally
dividually driven using battery-powered electric motors. A joined at its center to the stationary plate member 29 by a
suitable two-speed drive system for each wheel of the vehicle 35 pivot pin 35. A portion of the upper edge of the stationary
would enhance the mobility and usefulness of the vehicle. plate member 29 is circular so that it corresponds to and is
flush with the circular plate member 33. Aligned notches 37
SUMMARY OF THE INVENTION and 39 are provided in the plates 29 and 33, respectively, and
The invention comprises a pair of power transmitting ,n a spring-urged latching pawl 43 reciprocates within the
wheels mounted diametrically opposite each other on a selec 4° "otchf ,37 and 39.to selectlve|y re'f* 'he pla* member 33
. . .. . . . T.U ~ . r.u • n u i • for rotation around the pivot pin 35. Two of the notches 39twely rotatable plate member. The first of the pair of wheels
 K afe fonned jn ^  ^ '^ „ ^ The ^
dnven by a motor drive shaft and the second wheel is dnven ,
 43 js mounted Qn the ,ate member £ b a bfacket 4|
by the first wheel through a larger intermediate step-down
 and is actuated through a cab)e 47 extending to the desired
wheel so that the second wheel turns at a slower rpm than the 45 operating location
first. A main drive belt passes around one of the plate- A drive shaft 51 has one end thereof rotatably mounted in
mounted wheels and a relatively large wheel sprocket that the plate member 33, and fixed to the drive shaft 51 is a power
may be attached to and thus drive a wheel of a vehicle. The transmitting wheel 53. The drive shaft 51 extends perpendicu-
plate member on which the pair of wheels are mounted is lar to the plate 33 to an electric motor 55 that selectively
selectively releasable for rotation and when the plate member rotates the shaft 51. The motor 55 is pivotally joined to a
rotates 180° the two wheels exchange positions and thus bracket 57 through a fitting 59 so that the motor may rotate
change the wheel that is engaged by the main drive belt. The eccentrically counterclockwise around an axis that coincides
pull force exerted by the main drive belt against the turning w'*h a line defining the rotational axis of the plate 33 as will be
plate-mounted wheel is used to rotate the plate. When the belt 55 explained hereinafter.
engages both of the plate-mounted wheels simultaneously dur- A sec°nd shaft 63 is rotatably mounted at one end in the
ing the shifting phase, the normally slower turning wheel is plate 33 and at the other end to the motor 55, extending paral-
permitted to turn faster through a ratchet mechanism. lel wth the dnve sh^ 51- T_he shaft 63 is merelV rotatably
Accordingly, it is a general object of the present invention mounted to.the housing of the motor 55 and is not directly
to provide a two-speed drive system that is simple, reliable and 60 dnven by the motor 55. Power transmitting wheel 65 equal in
low in maintenance requirements. *?*?* f"d lenSth to the whueel 53.» fixed'to the sha* 63'
A more specific object of the invention is to provide a sim- Th,e ™h£l <? over ^ ^ *«~fls J°'ned <° a ««$*™
, . _ . jj-
 f j- • uir u-i wheel 69 of larger diameter than the wheels 53 and 65. Theplified two-speed dnve system for driving a wheel of a vehicle
 ajf rf wheek 58 and 6§ and ^  shafts s, ^ 63 arg diametrj.
wherein the shift in speed is made by utilizing forces inherent
 6J cal]y ^^ wjth each other and wjth ,he pivot pjn 3J wjth
in the drive system thus avoiding the need for an external shift-
 the pivot pjn 35 being ,ocated midway between the shafts 51
ing force.
 and 63 -rhe pair of wheeis 53 and 65 are ^SQ -m a common
Another object of the invention is to provide a reliable and
 piane that extends perpendicular to the shafts 51 and 63.
lightweight two-speed drive system for driving individually A ratchet drive is incorporated between the wheel 65 and
driven wheels of a lunar surface vehicle which drive system 70 the step-down wheel 69. As shown in FIG. 5, the ratchet
requires a minimum amount of maintenance, is convenient to mechanism comprises a series of teeth 71 formed around the
shift, and is capable of being driven by an electric motor. inner surface of the step-down wheel 69 and a plurality of
These and other objects and advantages of the invention pawls 73 projecting from the wheel 65 and engaging the teeth
will become apparent upon reference to the following specifi- 71. As is apparent, the wheel 65 may turn clockwise within the
cation, attendant claims and drawing. 75 step-down sprocket 69, the reason for which will become ap-
3,678,771
parent in the forthcoming description of the operation of the
invention.
As shown in FIG. 1, a drive belt 75 passes around the wheel
drive sprocket 11 and the wheel 65. The outside surface of the
belt 75 passes over the idlers 27. A belt 77 passes around the
step-down wheel 69 and a portion of the wheel 53. The
remaining portion of the wheel 53 is not in contact with either
belt in the position shown in FIG. 1.
It is evident that the electric motor 55 may be positioned
very close to the wheels 53 and 61, making the shafts 51 and
63 very short. In FIG. 1 the motor 55 is shown spaced from the
wheels 53 and 61 primarily for purposes of clarity in the illus-
tration.
OPERATION
As shown in FIGS. 1 and 2, the drive system is in the low
speed position and the belts 75 and 77 would be moving in the
clockwise direction as indicated by the arrows. The drive shaft
51 of the motor 55 turns the wheel 53 clockwise which drives
the step-down wheel 69 through the belt 77. The step-down
wheel 69, being larger in diameter than the wheel 53, turns at
a lower rpm than the wheel 53. The wheel 65 turns at the same
rpm as the step-down wheel 69 since it is connected to the
wheel 69 through the ratchet mechanism shown in FIG. 5.
Thus in the position of FIGS. 1 and 2 the wheel 65 drives the
wheel sprocket 11 through the drive belt 75 at a relatively low
speed.
When it is desired to shift the drive system to the relatively
high-speed position illustrated in FIG. 4, the spring-urged
latching pawl 43 is retracted by the cable 47 to unlock the
rotatable plate 33 from the plate 29. Since the plate 33 is then
free to rotate, the wheel 65, turning in contact with the drive
belt 75, will cause the plate 33 to rotate counterclockwise
rather than forcing the drive belt 75 to rotate clockwise. Thus
the wheel 65 rolls along the inner surface of the drive belt. As
the plate 33 rotates counterclockwise the drive belt 75 will
contact simultaneously both of the wheels 53 and 65, as in-
dicated in FIG. 3, which shows the drive system in the transito-
ry .position between the low-speed and high-speed positions.
When the drive belt 75 is in contact simultaneously with the
wheels 53 and 65 it is necessary for both of these wheels to
turn at the same speed. The ratchet mechanism between the
wheel 65 and the step-down wheel 69 shown in FIG. 5 permits
the wheel 65 to turn clockwise within the step-down wheel 69
as the pawls 73 ride over the teeth 71. Therefore, the wheel 65
may turn at the same speed as the wheel 53 during the time
when both wheels are in contact with the drive belt 75 as
shown in FIG. 3.
When the drive assembly is in the transitory position of FIG.
3 the plate 33 has rotated substantially 90° counterclockwise
and will continue to rotate counterclockwise until it has
rotated 180° at which time it will be automatically locked to
the plate 29 by the spring-urged pawl 43 sliding into the notch
39. As previously indicated, the notches 39 are located 180°
apart on the rotatable plate 33. After the full 180° rotation of
the plate 33 the drive system will be locked in the high-speed
position shown in FIG. 4. In this position the drive belt 75
passes over the wheel 53 that turns at a high speed relative to
the wheel 65 over which the drive belt passed in the low-speed
position of FIGS. 1 and 2. The wheel 65 is not in contact with
the drive belt 75 in the high-speed position of FIG. 4 although
it is still turning at a relatively low speed.
To change the drive system back to the low-speed position
of FIGS. 1 and 2 it is only necessary to retract the latching
pawl 43 and the plate 33 will rotate another 180° causing the
pair of wheels 53 and 65 to exchange positions again. As the
wheels 53 and 65 exchange places to shift from one speed to
another the motor 55, supported by bracket 57, rotates eccen-
trically counterclockwise around an axial line passing through
the pivot pin 35 just as do the wheels 53 and 65.
In the high-speed position of FIG. 4 the drive system may be
driven in the reverse direction by reversing the motor 55.
However, in the low-speed position of FIGS. I and 2 the drive
system cannot be driven in reverse because the step-down
5 wheel 69 would thus be turning counterclockwise and the
ratchet teeth 71 (FIG. 5) would slide over the pawls 73
without transferring the required torque to the wheel 65.
I claim:
1. A two-speed drive system comprising:
10 a. a rotatable member pivotally joined to a supporting
member for rotation around a predetermined axis;
b. means for locking said rotatable member against rotation
around said predetermined axis;
c. a pair of power transmitting wheels mounted on said
15 rotatable member, said wheels being arranged for rota-
tion around axes parallel with said predetermined axis;
d. portions of said pair of wheels being in the same plane,
said plane being perpendicular to said parallel axes;
e. means for driving said pair of wheels, said means includ-
20 ing means for driving one of said wheels at a lower rpm
than the other of said wheels;
f. a third rotatable wheel disposed coplanar with said por-
tions of said pair of wheels and adapted to be driven
selectively by either of said pair of wheels;
25 g. a drive belt engaging said third wheel and one of said pair
of wheels;
h. the other of said pair of wheels being disengaged from
said drive belt;
1. means for selectively releasing said rotatable member for
30 rotation around said predetermined axis whereby said
rotatable member will rotate as said wheel engaging said
drive belt turns in contact with said belt.
2. The invention as defined in claim 1 wherein said pair of
wheels are of substantially equal diameter, said third wheel
35 being larger in diameter than said pair of wheels, the said
wheel being disengaged from said drive belt being disposed
between said third wheel and said one of said pair of wheels
engaging said drive belt. j
3. The invention as defined in claim 2 wherein said
40 predetermined axis of said rotatable member is located mid-
way between and in diametrical alignment with the axes of
rotation of said pair of wheels whereby said pair of wheels
exchange position upon 180° rotation of said rotatable
member, said locking means including means for automati-
45 cally locking said rotatable member after rotation of 180°.
4. The invention as defined in claim 2 wherein said means
for driving one of said pair of wheels at a lower rpm than the
other of said pair of wheels comprises a step-down wheel
joined coaxially with one of said pair of wheels, a drive belt en-
50 gaging said step-down wheel and the other of said pair of said
wheels, said step-down wheel being of larger diameter than
either of said pair of wheels.
5. The invention as defined in claim 4 wherein said step-
down wheel is joined to said one of said pair of wheels by
55 means including means for permitting said one wheel to rotate
at a different rpm than said step-down wheel.
6. The invention as defined in claim 2 wherein said means
for driving said pair of wheels includes an electric motor,
means for interconnecting said electric motor with one of said
60 pair of wheels whereby power is transmitted from said motor
to said one of said pair of wheels.
7. The invention as defined in claim 6 including means for
supporting said electric motor for rotation around an axis in
alignment with said predetermined axis.
65 8. The invention as defined in claim 2 wherein said rotatable
member comprises a circular plate, said predetermined axis
being located at the center of said plate, said means for
locking said plate against rotation comprising two diametri-
cally opposed notches in said plate.
70 , « * , »
75


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