Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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SPECIFICATION
This invention relates to a swivel caster or wheel.
It is known for a cart which is guided by a person not
riding on it to ha~e a pair of f-xed wheels and a pair of swivel
wheels. The fixed wheels are on a horizontal axle which is fixed
to the cart and unable to move relative to it. Each swivel wheel
is on a short hori~ontal axle which swivels about a pivot having
a vertical axis. This vertical axis is on the vertical plane
which is parallel to the wheel face and which bisects the wheel
tire. Also, the axis of the pivot is on a line which does not
intersect the axis of the wheel axle,the horizontal distance
between the two axes being the radius of swivel of the wheel
axle~ The bearing of the pi~ot is fixed to the cart body, and
the rotating part of the pivot is fixed to the wheel axle by
means of a bracket. Whith this arrangement the wheels swivel
when the operating person applies a sideways force to the Gart.
~owever, to enable the cart to be steered ~y these swivel wheels
the swivelling axles must follow the vertical pivots, ta~ing
their path, while the cart is moving, which is in any case their
natural tendency. This means that when the cart is moving between
forward and reverse directions the swivel wheels swivel through
half a revolution so that the axle of each swivel wheel can
assume a following position relative to that o~ its pivot as the
cart moves along in its new direction. Furthermore, if an attempt
is made to guide the cart so that it exactly re-traces its origi-
nal path while changing direction, each swivel wheel will swivel
half a turn in a random direction, that is, either clockwise or
counter clockwise, and at an unpredictab~e ins~ant~ shortly after
the c~ange in direction between forward and reverse. Therefore,
swi~el wheels o~ this type are unsatisfactory for some types of
cart, such as lawnmowers, over whose steering full control must
be kept by the operating person during c~anOes of d~rection
between forward and reverse, when the cart is required to exactly
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re-trace its path because, during its swivel through half a
turn, one of the wheels would possi~ly collide wit~ a fe~ce
or fall over the lawn ed~e into a flower bed.
I have found -that these disadvantages may be overcome ~J
placing the vertlcal pivot in a horizontal slideway which can
be situated withln the wheel rim envelope, is parallel to t~e
face of the wheel,and is supported, through bearings, by the
wheel axleO This arrangement permits the vertical pivot to travel
in a horizontal line ~etween two positions, each a~ equal dist-
ance from the wheel axle. The bearing of the vertical pivot isfixed to the cart, and the rotating member of the pivot i~ ~ixed
to a slider which can travelin the slideway. When the cart is
moving forward, the vertical pivot will be in its ~orward pos-
ition, that is, forward of, and leading, the wheel axle. '~hen
the cart changes to a reverse direction the pivot will travel
along the slideway to its aft position, that is, aft of, and
leading, the wheel axle. 3ecause the vertical pivot bearings
are fixed to the cart, when the pivot moves alon~ the slideway
the body o~ the cart and the two fixed a~le wheels move the
same distance as the pivot. The relative movement between the
vertical pivot and the swivel wheel axle occurs becaufie the
swivel wheel is stationary, that is, it cannot rotate on its
axle, while the pivot is travelling between its two positions.
The wheel is preven-ted from rotating during this time by two
helical spring clutches. If the vertical pivot is between its
forward and aft positions, both spring clutches are engaged, and
the wheel cannot rotate on its axle in either direction. If the
vertical pivot is at its forward or aft position, the appropriate
spring clutch will be released, permitting the wheel ~o rotate
on its axle in the necessary direction. This swi~el wheel arr~
angement allows t~e cart to change ~etween forward and reverse
without the swivel wheels swivelling hal~ a turn, an~ there~ore
gives the operating person better control o~ the swivel wheels.
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Furthermore, this arrangement, because the wheels need not be
capable o~ swivelling through a full turn9 allows both wheels
in a pair to be easily linked together which ensures that each
wheel of the pair swivels by the same amount. ~his advantage
permits better control on uneven ground and is particularly
useful when the cartwheels make contact with the ground after
leaving it, for example, after the cart has been carried, when
full control of the wheels can more quickly and easily be
acheived.
In drawings which illustrate embodiments of the invention,
Figure 1 is an elevation of one wheel, partly in section.
Figure 2 is an end elevation of this wheelg partly in section.
Fig~re 3 is a top plan view of this l,vheel, partly in section.
Figure 4 is a view, in isometric projection, of the spring
clutch arrangement.
Figure 5 is an elevation o~ a cart which illustrates the
relative positions o~ the vertical pivot and the swivel wheel
axles when the cart is moving in the forward direction.
Figure 6 is an elevation of a cart which illustrates the
relative posi-tions of the vertical pivo-t and the swivel wheel
axles when the cart is moving in the reverse direction.
The wheel illustrated comprises a horizontal bar 1, one end
of which is fixed to the cart body and the other end welded to
a pair of ~rackets 2 which are attached by screws to the top9
non-rotating member of a thrust ball bearin~ 3 whose axis of
of rotation is vertical. If requiredfor cheapness, a plain
bearing could be usedO The bottom, rotating member of the bear-
ing has a bracke-t attached to it .vhich holds two identical shafts
4, whose axes are harizontal and parallel to each other. Carried
~y each sha~t, and free to rotate on it,is a pair of rolle~s 5.
The horizontal bar 1, brackets 2, bearin~ ~, shafts 4 and rollers
5 form a carria~e which is constrained by slideway 6 to tra~el
in a horizontal line which is parallel to the wheel Iace 7. The
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vertical axis of the thrust bearing 3 is on a vertical plane
which is parallel to the wheel face 7 and ~hich bisects the
tire 8. The guideway has a stop 9 at each end, shown in -the
drawing as a porti~n of the guideway bent round, to ~revent the
carriage from touching the wheel rim 10. The bottom part of the
guideway is extended and hent upward to form an outer plate 11
hich is parallel and adjacent to the outer face 7 of the wheel.
This outer plate 11 has a clearance hole for a piece of tubing 12.
The tubing is co-axial with the tire 8 and is fixed by welding
to the outer face 7. Within the tubing, co-axial with it, and
separated from it by bushing 13 is a non-rotating axle 14. The
axle has a shoulder 15, or other constraining device, at the
outer end, and tG the inner end is attached, b~ a screw, an inner
plate 16. The length of the tubing 12 is slightly shorter than
the distance between the shoulder 15 and the inner plate 16 so
that the wheel is ~ree to rotate, subject only to the constraints
of the spring clutches 17. The inner plate 16 is attached ~y
three scre~s, one at its centre, which attaches it to the axle lL~
~y means of a threaded hole in the axle, and one at each end,
each of ~hich attaches it to a spacer 1~, one end of which has
a threaded hole, and the other end of which is attached by weld-
ing to the outer plate 11. The spring clutch arrangement consists
of two identical close-wound helical springs 17 whose internal
diameter, when the springs are free, is slightly smaller than
the external diameter of the tubing 12. Each end o~ each spring
is extended in a straight line which is perpendicular to the
longitudinal axis of the helical portion of the spring, and both
ends of each spring are formed such that the angle subtended by
them in the plane which is perpendicular to the axis of the
helical portion is less than 1~0 degrees and more than 90 degrees~
the exact angle in any particular case depending upon the requir-
ed diameter of the wheel rim. The spring clutches 17 are sit~ated
on the tubing 12 and the inside of the spring heli~ ~rips the
outside of the tubing. The spring nearest the outer plate 11 is
arran~ed such that the spring end adjacent -to the o~ter plate is
horizontal, ~nd the other end is pointing downward. The horizon-
tal end is attached to the outer plate ~y a suitable clamp 1~,
and the downward pointing end left free. The spring nearest the
inner plate 16 is arranged such that the spring end nearest the
inner plate is horizontal, and the other end is pointing down-
ward. The horizontal end is attached to the inner plate by a
suitable clamp 19, and the downward pointing end left free. The
downward pointing, free end of each spring can be raised slightly
by a stri~er 20 which is fixed to the hori~ontal bar 1. If the
striker ls not in contact with either of the downward pointing
spring ends the wheel cannot revolve on its a~le in either
direction. If the free end of a spring is raised slightly the
helical portion of that spring becomes loose on the tubing 12
and the wheel is ~ree to rotate in one direction, but the other
spring, whose downward pointing end remains free, will continue
to grip and ~revent the wheel from rotating in the other direct-
ion~ It is in the nature of the usual spring clutch, which hasonly one helical spring, to allow rotation in one direction but
not in the other. In this invention, two spring clutches and a
release device are used to change the direction in which rotation
is allowed. Although it is possible, in the case of a three
wheeled cart, to have only one swivel wheel, most carts, being
four wheeled, will have a pair o~ swivel wheels, in which case
it is desirable that both of them swivel at the same time9 in the
same direction, and by the same amount. To ensure that this
happens, both swivel wheels in a pair are linked to each other
by two links, in this invention. Each link 21 is of the same
length. Each wheel has attached to its inner plate 16 two bear-
ings Z2 for pivots having vertical axes. ~or maximum rigidity
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the horizontal dis-tance between the vertical pivots on a wheel
should be as large as possible, within practicable limits. Free
to rotate in each bearing is a pin 227 and attached to this pin
is one end of one of the links 21~ As well as ens~ring that both
wheels of a pair swivel together, these two links ensure that
both thrust bearings 3 in a pair of wheels are in the same
position along their slideways.
