Note: Descriptions are shown in the official language in which they were submitted.
I
Title: WHEEL
10011 This technology relates to wheels for use in a non-earth
environment, for example on a lunar rover, for traversing over the moon
regolith.
[002] Some of the desiderata for such a wheel may be summarized
as:
- the wheel should be all metal;
- the tread should be compliant and able to conform elastically
resiliently to surface features which are highly uneven, and
include sharp-edged pebbles, stones, rocks, etc;
- the wheel, as a unitary structure, should be lightweight but strong;
- the particles of the moon regolith, being electrostatically charged,
tend to adhere, and the arrangements of the components of the
wheel should avoid nooks and crannies in such locations that an
agglomeration might affect performance of the wheel;
- the components of the wheel that move relatively should be spaced from
each other to minimize the opportunity for contact, the friction
from which might impair performance;
- the wheel should be able to accommodate abusive impacts and shock-
loads, such as arise due to bumps and falls, when transporting
designed loads;
- the wheel should retain structural integrity despite wide, and
sometimes rapid, variations of temperature.
[003] LIST OF THE DRAWINGS
Fig.l is a pictorial view of an all-metal wheel that embodies claim 1.
Fig.2 is a side-elevation of the wheel of Fig.l.
Fig.3 is a plan-view of the wheel of Fig.l.
Fig.4 is the same view as Fig.1, but omits many of the components, for
illustration.
Fig.5 is the same view again, but omits more of the components.
Fig.SA is a diagram confirming the axes of the three rotational modes of
movement with respect to the axis of the vehicle.
Fig.6 is cross-sectional view of the wheel of Fig.l, taken on the line
VT-VI, omitting some of the components.
Fig.7 is a plan view of the components shown in Fig.6.
Fig.8 is a view from the left, of the components shown in Fig.6.
Fig.9 is a pictorial view of another all-metal wheel that embodies
claim 1.
Figs.10,11,12 correspond to Fig.9, as Figs.2,3,4 correspond to Fig.l.
F1g.13 is a side-view showing some of the tread components of the wheel.
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Fig.14 is a diagrammatic plan view of the wheel of Fig.9, shown as if
the circumference of the wheel were laid flat.
[004] In the exemplary wheel 20 shown in Figs.1-8, tread-plates 21
comprise individual pieces of sheet-titanium, which are bent upwards to
create traction-lugs or grousers 23 (two per tread-plate). As shown,
the resulting tread is aggressive, and designed to give good traction
and grip on the moon surface. Also, the bent-up grousers 23 add
strength and rigidity to the tread-plates 21, which enables designers to
specify that the sheet metal (e.g titanium) of the tread-plates can be
thin.
[005] The ends of the tread-plates are formed with side-lugs 25,
which serve to provide centralizing alignment for the wheels when
rolling over rough terrain.
[006] The leaf-spring 27, as shown, has a considerable length.
This means that the leaf-spring 27 can readily be designed such that the
distal end of the leaf-spring can deflect a distance of e.g two cm,
under load, at a more or less constant (and relatively low) rate,
without the spring being overstressed. It may be noted that the
deflection of the leaf-spring, radially inwards, is limited in that the
leaf-spring bottoms against the outer radius of the rim of the rim-
spokes-hub-unit 29 of the wheel 20, if overloaded.
[007] This protection against overloading enables the spring
designers to set the spring force and spring rate of the leaf-spring 27
to suit the normal loading and suspension travel required of the
wheel 20, without having to compromise these parameters to cater for the
abuse condition. (However, the designers should make the springs
sufficiently strong that the abuse condition occurs only rarely.)
[008] Generally, all the suspension movement takes place in the
wheel (i.e the vehicle makes no provision for the axles to move up/down
relative to the body of the vehicle) by deflection of whichever one(s)
of the tread-spring/ tread-plate unit(s) are in touching contact with
the ground. Each tread-plate 21 moves predominantly radially with
respect to the axis of the rim-spokes-hub-unit 29 of the wheel 20, as it
takes the load. Because of the way the leaf-spring 27 and its mounting
bracket 30 are configured, the up/down movement of the tread-plate 21,
under load, is basically directly radial. The leaf-spring 27 is bolted
flat-on to the mounting face of the bracket 30, and thereby constrains
the tread-plate 21 to move radially, and inhibits the tread-plate
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against rotating, tipping, and twisting.
[009] At the same time, the leaf-spring 27 is somewhat compliant
in the tipping and twisting modes, whereby, over rough terrain, the
tread-plate 21 can accommodate itself to the unevenness of the ground.
(The manner in which the tread-plates cope with modes of movement other
than up/down movement is explained later.)
[0010] Thus, each tread-plate 21, as it takes the load, moves
predominantly radially (i.e radially relative to the axis of the
wheel 20) -- but if tipping and twisting should be required, those modes
of movement can take place. The shape of the leaf-spring 27 ensures the
tread-plate 21 is returned or reset back to its unstressed neutral
position as the tread-plate 21 becomes once again unloaded.
[0011] It may be noted that the deflection movements of the tread-
plate 21 and the leaf-spring 27 take place substantially without
friction. The contact between the grousers 23 and the ground surface
involves some slippage of the edges or tips of the grousers over the
ground material, in which some friction will be induced, but the
deflection of the tread-plate 21 against the resilience of the leaf-
spring 27 is basically frictionless. (It may be noted that a railway
wheel on a metal track experiences considerably less rolling resistance
than, say, an inflated rubber tire on an asphalt road: the rolling
resistance of the wheel in the drawings is more closely comparable to a
railway wheel than to a rubber tire.)
[0012] It is not suggested that there will be no rolling-resistance
to the motion of the wheel 20 over the ground. The edges or tips of the
grousers 23 will slip and slide relative to the ground, especially when
the ground is uneven, and the tips will become abraded as a result.
[0013] The grousers 23 make the tread of the wheel very aggressive
in the traction (forwards-backwards) direction, but the tread has little
aggression in the sideways direction. If designers contemplate that
sideways aggression of the treads should be increased (to provide a
"keel" to maintain directional stability over e.g cambered terrain),
lugs can be provided that are in the same plane as the side-lugs 25, but
protrude radially outwards, rather than inwards. Alternatively, the
designers can arrange the grousers, or the tread-plates, in e.g a
herringbone pattern.
[0014] The wheel technology as described herein can be applied when
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the wheels are conventionally steered (i.e at least one of the wheels on
the vehicle is steer-pivoted about a yaw-axis of the vehicle), and can
be applied when the vehicle is skid-steered (i.e provision is made for
driving the left wheels at a different rpm from the right wheels). In
the case of skid-steering, it can be beneficial for the resistance of
the individual wheel to lateral slippage to be smaller than in the case
of yaw-steered wheels.
[0015] The leaf-spring 27, being in sheet form, has good rigidity
in the plane of the sheet (i.e in the yaw-mode -- see Fig.5A). Thus,
the tread-plates 21 are held firmly in their desired orientations
relative to the wheel as a whole, and relative to each other, as each
tread-plate 21 in turn deflects under the load on the wheel. Again, the
tread-plates are so structured and arranged that they cannot touch each
other, during operation of the wheel.
[0016] The tread-plates 21 are constrained to maintain their
predetermined circumferential spacing, not only by the geometry of the
leaf-springs 27, but by wire cables 32, to which each tread-plate 21 is
clamped. The cables 32 are of fixed hoop-length. The hoop-cables 32
are not elastic.
[0017] The hoop-cables 32 are arranged such that the leaf-
springs 27, acting on the tread-plates 21, keep the cables 32 under
tension. The manner in which the sizes of the hoop-cables are related
to the spring-rates of the tread-spring, and to the forces and
deflections required of the tread-springs, may be explored as follows.
[0018] Three positions or conditions of the tread-spring are of
interest, namely:
- the no-stress position of the tread-spring, which occurs when the
hoop-cables are not present on the wheel;
- the cable-taut position of the tread-spring, which occurs when the
hoop-cables are in place and the wheel is unloaded (this is the
position shown in Fig.6); and
- the bottomed-out position of the tread-spring, which occurs when the
tread-unit is under heavy load, and has bottomed out against the
rim.
[0019] The overall-deflection-capability of the tread-spring is the
travel of the spring between its no-stress position and its bottomed-out
position. The actually-enabled-deflection of the tread-spring is the
travel between its cable-taut position and its bottomed-out position.
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[0020] Typically, the designers will so configure the components of
the wheel that the actually-enabled-deflection of the tread-spring is
about half of the overall-deflection-capability of the tread-spring.
Expressing the preferred limits in this regard, the actually-enabled-
deflection of the tread-spring should be between thirty percent and
seventy percent of the overall-deflection-capability of the tread-
spring.
[0021] As will be understood from Fig.6, the angle of the tread-
plates to the horizontal will change as the spring deflects. Typically,
designers will configure the tread-units and the hoop-cables such that
the tread-plates are substantially horizontal (i.e as shown in Fig.6)
when the springs are in their cable-taut position.
[0022] The tread-plates 21 and the leaf-springs 27 form tread-
units, comprises the assembly of. The spring-brackets are unitary
with the components of the rim-spokes-hub-unit 29. As shown, in
Figs.1-8, there are as many leaf-springs as tread-plates, and the leaf-
springs correspond to the tread-plates on a one-on-one basis. Other
arrangements are contemplated, in which e.g two tread-plates share one
leaf-spring, or one tread-plate is shared by two leaf-springs.
[0023] The unstressed mass of springs and tread-plates hold the
cables in place in a highly stable manner, even though the bottom tread
is deflected radially inwards (and the tread-unit and cables are
flexible enough to deflect inwards at the bottom
[0024] The leaf-spring 27 can deflect to allow its tread-plate 21
to move radially (with respect to the wheel axis) about the roll-axis
(which is the main suspension movement), and to allow the tread-plate to
rock about the pitch-axis, as will occur when moving over uneven ground.
But rotation or twisting of the tread-plate about the yaw-axis is firmly
resisted by the geometry of the spring, and by the presence of the wire-
cables.
[0025] In the alternative wheel shown in Figs.9-14, there is only
one hoop-set of tread-plates 41, and the tread-plates 41 span right
across the width of the wheel 40. Each tread-plate 41 is supported by
two tread-springs 47.
[0026] The single tread-plates 41 of the wheel of Figs.9-14 are a
little less compliant than the separate left and right tread-plates of
Figs.1-8, in respect of traction-engagement with uneven ground.
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[0027] Another difference is that each tread-plate 41 forms a
triangle with its two tread-springs 47. This may be contrasted with the
tread-plate 21, which is supported by its single tread-spring 27 in
cantilever mode. Thus, the tread-plate 41 is positioned or located with
respect to the rim-spokes-hub-unit 29 considerably more robustly than is
the tread-plate 21. The suspension travel, spring-rate, etc are, or can
be, the same in both designs.
[0028] As may be understood from Fig.13, the long tread-plate 41,
in spanning over the rim of the wheel, is provided with a travel stop in
respect of the up/down suspension movement, in that the tread-springs 47
cannot deflect beyond the point at which the tread-plate 41 bottoms out
against the rim. (In the Figs.1-8 design, the tread-plates could also
bottom against the rim.)
[0029] In the Figs.9-14 design, the hoop-cables 32 are clamped to
the tread-plates 41 using the same bolts that clamp the tread-springs 47
to the tread-plates 41.
[0030] It may be noted that, in the wheels depicted herein, there
are no moving pivots, nor any points at which components of the wheel
might rub together. All the movements performed by the wheel are guided
and constrained by the tread-springs and the hoop-cables, without any
rubbing contact between components.
[0031] Thus, the tread-springs perform the dual function of
providing resilient deflection capability, to enable suspension and
other movements, and at the same time the tread-springs keep the various
components in their correct geometrical relationships. In this latter
function, the tread-springs are assisted by the hoop-cables. Thus, the
hoop-cables permit the leaf-springs to be designed primarily to have the
desired deflection characteristics, without the need to compromise
because of the need to hold the components in their positions_
[0032] The configuration of the hoop-cables and of the leaf-
springs, and the manner of mounting the springs to the rim, and of
mounting the tread-plates to the leaf-springs, as shown, combine to
create very good resilience over a long radial travel of the tread-
plate, and to create good compliance which enables the tread-plate to
accommodate itself to the uneven ground. At the same time, the tread-
plates are firmly constrained against moving away from their pre-
determined positions relative to each other. The tread-plates can be
mounted fairly closely together, but there is little risk of the tread-
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plates touching each other.
[0033] Of course, the wheels must be capable of operating over
uneven ground, climbing slopes, coping with adverse cambers, and so on.
The tread-plates must cope with terrain that subjects the plates to
twisting and tilting, including traversing over rocks small and large.
The wheel must not lose traction.
[0034] The desired movements include:
- the main suspension movements, i.e up/down deflections of the tread-
plates (along the yaw-axis of the vehicle) as they contact the
ground once per revolution of the wheel, which involves simple
bending of the leaf-spring about the roll-axis.
- tipping/rocking of the tread-plates about the pitch-axis, which
involves the leaf-spring undergoing twisting deflection about the
pitch-axis.
[0035] Movements to be resisted include:
- circumferential movement of the tread-plate in response to traction
forces on the tread-plate. The illustrated layout puts these
forces in the plane of the sheet metal of the leaf-spring, which
maximizes the resistance of the leaf-spring to circumferential
deflection. However, given that the leaf-spring is light and
thin, the leaf-spring would or might buckle under heavy traction
(or braking), in the absence of preventive measures (e.g in this
case, the provision of the hoop-cables)
[0030 The manner in which the hoop-cables interact with and assist
the leaf-spring, during operation, may be related to the different modes
of movement of the tread-plate, as shown by the following tabulations.
[0037] Pitch-mode tipping of the tread-plate:
what need for flexibility/rigidity?
- good flexibility - for tread compliance on uneven ground.
what does the leaf-spring provide?
- the leaf-spring provides the good flexibility.
might the leaf-spring buckle in pitch-mode, without cables?
- no
do the cables help prevent buckling in pitch-mode?
- no, but buckling not likely.
[0038] Roll-mode movement of the tread-plate:
what need for flexibility/rigidity?
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- good flexibility - this is the main suspension movement.
what does the leaf-spring provide?
- the leaf-spring provides the good flexibility.
might the leaf-spring buckle in roll-mode, without cables?
- no
do the cables help prevent buckling in roll-mode?
- no, but buckling not likely.
[0039] Yaw-mode twisting of the tread-plate:
what need for flexibility/rigidity?
- good rigidity required for traction (and braking), to
resist yaw-twisting.
what does the leaf-spring provide?
- the leaf-spring resists yaw-twisting.
might the leaf-spring buckle in yaw-mode, without cables?
- yes, the leaf-spring likely would buckle under yaw-mode
twisting.
do the cables help prevent buckling in yaw-mode?
- yes, the cables add to the rigidity with which the leaf-
spring resists yaw-mode twisting and buckling.
[0040] Without the cable, the leaf-springs could hardly be designed
to have the required low-rate flexibility to provide up/down suspension
movement (roll-mode rotation of the leaf-spring), and yet strong enough
not to buckle under yaw-mode twisting of the leaf-spring.
[0041] The hoop-cable retains its circumferential position,
relative to the rim, very rigidly. That is to say, the hoop-cable
cannot move circumferentially with respect to the rim. In the Figs.1-8
wheel, there are thirty-one tread-plates attached to each hoop-cable
(being sixty-two tread-plates per wheel).
[0042] When the wheel is under load, at least one, and assumedly
perhaps three, of the hoop-set of tread-plates will be making actual
touching contact with the ground. Thus, the positional-rigidity of the
cable arises because the hoop-cable is attached to the twenty-eight
tread-plates that are clear of the ground. The result, as far as the
three tread-plates that are in contact with the ground are concerned, is
that the rigid retention of the position of the cable relative to the
rim is enough to over-ride any tendency of the distal ends of the three
tread-plates to move out of circumferential alignment. The heavier the
traction forces, the greater the forces tending to make the distal ends
of the tread-plates move circumferentially.
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[0043] At the same time, the cables do not inhibit or interfere
with the suspension (roll-mode tipping) movements of the plates. The
cables also do not interfere with pitch-mode tipping movements, and it
can be beneficial for the tread-plates to be able to tip or rock in the
pitch-mode, for good traction on rough ground.
[0044] When a particular tread-plate is in contact with the ground,
the ground-contacting tread-plate will move radially inwards, as the
leaf-spring deflects in the roll-mode. It follows that the inwards-
moving ground-contacting tread-plate and its neighbours will move
towards each other in the circumferential sense. The tread-plates
should be positioned far enough apart, circumferentially, that they do
not touch.
[00451 When the neighbouring ground-contacting tread-plates
approach each other circumferentially, as a result of suspension
movement, of course the portion of the hoop-cable between those tread-
plates slackens. Thus, the hoop-cables do not absolutely prevent the
tread-plates (and the tread-springs) from undergoing yaw-mode
deflection. Rather, the hoop-cables act to prevent the tread-springs
from over-deflecting, away from their natural or unstressed positions,
to the extent that buckling of the tread-spring might be a problem.
[0046] Thus, the strength and rigidity of the thin, light, leaf-
spring is enough to cope with the minor deflections permitted by the
slackness of the hoop-cables. The cables prevent (i.e inhibit) buckling
under gross deflections.
[0047] In short, the individual tread-springs are thin and light,
and vulnerable to being damaged by gross distortions due to traction
forces on the bottom tread-plates. But the hoop-cable makes the
combined strength and rigidity of all the other (light) tread-springs
available to assist the tread-spring of the ground-contacting tread-
plate to support heavy traction forces_ Notionally, only one of the
tread-units undergoes suspension deflection at one time. But the cable
is attached to all thirty-one, which leaves say twenty-eight tread-units
still holding the cable steady. Thus the cables themselves are highly
resistant to moving out of their desired position.
[0048] It might be possible to design the tread-springs to have
enough strength such that each tread-spring on its own without
mechanical support -- via the hoop-cables -- from the other tread-
springs would be able to cope with the desired tipping/ rocking/
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twisting movements of the tread-plates. However, tread-springs that
were indeed able to support themselves in that manner would not be the
light, thin, flexible, leaf-springs as depicted herein. The hoop-
cables, by linking all the tread-plates together circumferentially,
enable the tread-plates to support each other against any
circumferential deflections.
[0049] The wheel of Figs.1-8 has two hoop-sets of tread-units,
being left and right hoop-sets. A left hoop-cable connects the thirty-
one tread-plates of the left hoop-set, and a right hoop-cable connects
the thirty-one tread-plates of the right hoop-set. The left tread-
springs span over the rim, being fast to brackets on the right side of
the rim, while the right tread-springs also extend over the rim, being
fast to brackets on the left side of the rim. Thus, the tread-springs
can be of a good length, as required in order to provide good deflection
characteristics. In fact, from this standpoint, preferably the flex-
length of the tread-springs is half the overall width of the wheel, or
more.
(0050] This same preference for the flex-length of the tread-
springs to be half the overall width of the wheel or more is achieved
also in the wheel of Figs.9-14.
(0051) The wheel of Figs.9-14 has only one hoop-set of tread-units.
The thirty-one tread-plates extend across the width of the wheel. Left
and right hoop-cables connect the outer ends of the tread-plates.
[0052] In Figs.9-14, there are again sixty-two tread-springs, but
now disposed two per tread-plate. The tread-springs do not span over
the rim, but rather the left tread-springs are fast to brackets on the
left side of the rim. The desired long flex-length of the springs is
achieved by setting the springs at an angle. In addition to enabling
the springs to be of a good length, setting the springs at an angle has
the effect of triangulating the tread-unit, whereby the tread-plates are
supported against circumferential movements relative to the rim very
strongly and rigidly, even without the hoop-cables.
[0053] Designers might prefer to attach the tread-springs directly
to the sides of the rim of the rim-spokes-hub component. However, the
provision of the brackets means that the plane of the sheet metal of the
leaf-spring lies in the best orientation to ensure that suspension-
deflection of the spring can take place smoothly and with little chance
of adverse distortions of the sheet metal.
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[0054] As mentioned, in both wheels, under heavy suspension
deflection, the tread-unit is protected from possibly-damaging
distortions by bottoming against the rim. In the Figs.1-8 wheel, it is
the tread-springs that actually make contact with the rim, whereas in
the Figs.9-14 wheel, it is the tread-plates that make contact with the
rim; designers might consider that the tread-plate would be more able to
withstand forceful contact with the rim than the tread-spring.
[0055] It is recognized that, in the wheels as depicted, the leaf-
springs can be so configured as to create favourable suspension and
strength characteristics. In particular, the leaf-spring has a
thickness-dimension which lies predominantly radially with respect to
the wheel. Also, the width-dimension of the leaf-spring lies in a plane
that is predominantly tangential with respect to the wheel. (The word
predominantly, here, signifies that the dimensions have major components
in the said directions.)
10050 Preferably, the portion of the tread-spring that, in
operation, is capable of undergoing resilient deflection, has a flex-
length that is half the width of the wheel, or more.
[0057] As shown in Fig.6, the line 34 is a tangent drawn at a point
on the curved surface of the line leaf-spring 27. The tangent 34 lies
at an angle 36 to a line that is parallel to the axis of the wheel.
Preferably, at any point on the flex-length of the leaf-spring, the
angle is thirty degrees or less.
[0058] Preferably, the spring is also so disposed, in the wheel,
that the thickness dimension (i.e the distance between the surfaces of
the sheet material) is aligned with a radius of the wheel, or lies
within thirty degrees of a radius.
[0059] Each point on the flex-length of each leaf-spring has a
tread-spring radius, being a radial line joining the wheel-axis to that
point of the tread-spring, and preferably the tread-unit is so mounted
with respect to the rim that the plane of the sheet metal of the tread-
spring at the point lies within thirty degrees of being perpendicular to
the tread-spring radius at the point.
[0060] A wheel-radius of a point in the wheel is a line that is
perpendicular to the wheel-axis, and extends from the wheel-axis to the
point, and preferably the wheel-radius of the proximal end of the leaf-
spring is shorter than the wheel-radius of the distal end.
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[0061] In respect of each tread-unit, preferably the or each tread-
plate has no physical attachment to the rim except through the
respective tread-springs, and preferably the hoop-cables have no direct
physical connection to the rim.
[0062] The numerals used in the drawings are listed as:
20 wheel
21 tread-plates (sheet titanium)
23 traction-lugs or grousers of tread-plates
25 side-lugs of tread-plates
27 leaf-springs or tread-springs (spring steel)
29 rim-spokes-hub unit
30 spring mounting rim-brackets
32 hoop-cables
34 tangent to leaf-spring 27
36 angle of tangent
41 tread-plates
43 grousers
47 tread-springs
50 spring mounting rim-brackets.
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