Universal ski boot heater

A universal ski boot heating system, includes a boot assembly and a power pack assembly. The boot assembly employs a heating element disposable in a ski boot and electrically connected to a boot anchor secured to the exterior of the boot. The power pack assembly includes an elecrical energy source and means for engaging the boot anchor to permit selective contact between the energy source and the heating element through rotation of the power pack assembly when engaged with the boot anchor.

BACKGROUND OF THE INVENTION 
The present invention relates generally to electrical heating systems for 
footwear, and specifically to a universal heating system adaptable to ski 
boots of any design and manufacture. 
Cold, and specifically cold feet, has been a major limiting factor in the 
ability of the outdoor sportsman to appreciate and enjoy winter sports. As 
technology has improved throughout the years, fleece-lined leather boots 
have given way to footwear constructed using various synthetic shell 
materials and foam, Thinsulate.TM. and other insulations. This improved 
winter footwear has benefited skiers, who now enjoy a variety of rigid 
boot shell designs insulated with the aforementioned materials. However, 
since downhill or alpine skiers spend extended periods of time outdoors, 
two major problems still inhibit foot warmth, one being a function of the 
nature of the sport and the second of advances in boot technology. The 
first phenomenon referred to above involves the long periods of relative 
inactivity while skiing, attributable to lift lines and long lift rides, 
the latter on chair lift chairs which inhibit blood circulation to the 
lower extremities. The second phenomenon is associated with boot 
technology advances in the areas of foot retention and responsiveness of 
the boot and attached ski to body movement. Even though many different 
lasts are available for ski boot inner shells, and custom lasts are 
relatively inexpensive for the benefit gained, many skiers tighten their 
boots to an extraordinary degree to give better ski control and feedback 
from the ski through the foot, ankle and calf regions of the leg. This 
tightness constricts the foot and ankle regions, restricting blood flow 
thereto and contributing to cold feet. 
Ski racers, like other skiers, experience the above-mentioned problems. 
However, the adverse consequences of cold feet to their performance is 
even more dramatic at high racing speeds where the "feel" of the skis and 
terrain is all-important to promote optimum times and avert catastrophic 
injury. 
Since completely insulated ski boot structures would be massive and 
unwieldy, many efforts have been made to artificially provide heat, 
generally electrical, to the feet. For example, U.S. Pat. No. 4,080,971 
discloses a calf-mounted battery pack having a wire extending to a 
footwear insole incorporating a resistance heating element. This device is 
obviously inappropriate for skiing, as the bumps and shocks encountered as 
well as calf flexing would cause the battery pack to slip down the leg in 
short order. U.S. Pat. No. 4,837,494 discloses a ski-mounted battery pack 
including a wheel-type generator for battery recharging, the battery pack 
providing power to a resistance element in a ski boot through a connecting 
cable. The battery pack and generator weigh down and unbalance the ski, 
and the presence of cable connectors is a safety hazard to proper binding 
operation and to a total boot from ski release. 
Several designs have been proposed for incorporating batteries in the ski 
boot structure itself. U.S. Pat. Nos. 3,977,093 and 4,507,877 each 
disclose batteries housed in boot or shoe soles, powering resistance 
heater type insoles. These designs render it virtually impossible to 
remove and replace batteries during a day of skiing, and additionally 
require specialized footwear designs having battery cavities. 
Additionally, the on/off switch of the '093 patent is inside the boot and 
activated by the heel of the wearer, preventing its being turned off. The 
'877 switch is on the exterior of the boot, and thus susceptible to water 
incursion and icing problems, as well as impact damage from skier falls. 
U.S. Pat. No. 4,798,933 discloses another design, one of the type commonly 
seen in commercially-available heated ski boots today. This design uses a 
molded cavity in a bulge on the back of the ski boots to accommodate 
batteries, but there is no access to remove same except from the inside of 
the boot after the inner bladder or soft shell is removed. Again, as with 
the designs previously mentioned, the on/off switch is on the exterior of 
the boot. 
U.S. Pat. Nos. 4,697,359 and 4,780,968 disclose several variations of a ski 
boot design with integral heater, wherein a plug-in type battery pack is 
housed in cavities or apertures which can be located on the back, instep 
or top front of the boot. The '359 patent discloses a battery pack having 
only contacts for plugging into the boot, the switch for turning the 
current on or off being included in the boot structure. The '968 
embodiment includes the switch in the battery pack. The disadvantage of 
the foregoing designs resides in the necessity of special boot shells to 
accommodate the battery packs, and of fragile switches susceptible to 
icing as the boots become wet and then freeze during wear. 
A more versatile boot heater design is disclosed in U.S. Pat. Nos. 
3,859,496 and 3,946,193, wherein a battery case is mounted on the heel or 
back of a ski boot having a metal mounting plate thereon, and the heater 
is turned on and off by moving the battery pack up and down on the 
mounting plate on rails between an on and an off position. While this 
design is usable on any ski boot to which a mounting plate has been 
affixed, the use of electrical contacts on the exterior of the battery 
pack can result in shorts from water on the mounting plate or battery 
pack, and the boot wearer has to ascertain whether the heater is on or off 
by experimentally sliding the packs up or down on the plates, waiting to 
see if his feet get warm, or having a companion switch to turn the device 
on or off or observe which position the pack is in on the plate. Moreover, 
the mounting plate is itself mounted on a bracket secured to the ski boot, 
leaving the wires to the contacts exposed to the weather as well as build 
up of water, snow and ice, which accelerates deterioration thereof. 
Finally, the heating element is electrically connected to the mounting 
plate contacts via screws accessible only from the boot interior, making 
easy removal of the insole or boot liner impossible. 
In short, the boot heaters of the prior art suffer from either reliability 
problems, operational problems, or manufacturing complexities which render 
them all inadequate in solving the problem of cold feet in an economical, 
reliable manner. 
SUMMARY OF THE INVENTION 
In contrast to the prior art, the ski boot heating system of the present 
invention provides reliability and simplicity as well as economic design. 
The ski boot heating system of the present invention comprises a boot 
assembly and a power pack assembly. The boot assembly includes a heating 
element in the form of a flexible circuit substrate having an electrical 
resistance circuit thereon which extends from the top front of the boot 
insole, around the tip and back down the insole bottom where it may 
terminate at wires exiting the side or bottom of the boot bladder or inner 
shell, or alternatively it may extend out through a slit in the heel of 
the boot bladder or inner shell to the upper heel of the boot shell. In 
either case, the heating element is electrically powered via 
disconnectable contact pin means extending from the inside of the boot 
through the back or heel of the ski boot into contact post means secured 
in a non-conductive boot anchor securely fastened to the exterior of the 
boot heel or back. The boot anchor includes a plurality of 
radially-extending lugs, tabs or protrusions. The power pack assembly 
includes a case containing an electrical power source in a compartment, 
preferably two rechargeable Ni-Cad sub "C" cells connected in series via a 
shunt and contacted by two battery spring contacts extending into a cavity 
at the base of the case, the cavity having an open aperture defined at its 
periphery by a series of slots or discontinuities adapted to receive the 
like-shaped lugs, tabs or protrusions on the boot anchor. An elastomeric 
sealing element may surround and extend downwardly from the periphery of 
the cavity opening, and compressively seal against a continuous lip or 
flange protruding laterally from the boot anchor below the lugs when the 
power pack assembly is placed over the boot anchor so that the boot anchor 
lugs or protrusions are aligned with the slots or discontinuities. 
Alternatively, a flexible donut may surround the aperture inside the 
cavity to exclude ice, snow and water. 
To engage the boot anchor with the power pack, the power pack is rotated 
thereon after the lugs enter the case slots, a wave spring washer inside 
the case cavity being compressed by the intruding boot anchor so as to 
firmly hold the case in position. If the case is rotated 90.degree. in 
either direction, the case is locked to the boot anchor, but the heating 
system remains inoperative as the spring contacts do not engage the 
contact posts protruding through the center of the boot anchor. Further 
90.degree. rotation in the same direction as the initial rotation results 
in the completion of the electrical circuit between the batteries in the 
power pack assembly and the heating element in the boot assembly.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIGS. 1 and 3 of the drawings, a first preferred 
embodiment of the boot assembly 10 of the present invention will be 
described in detail. Boot assembly 10 includes a flexible printed 
electrical resistance circuit heating element 12 to provide heat to the 
foot of the boot wearer. The heating element 12 depicted in detail in 
FIGS. 13, 14 and 14A is electrically connected through the upper heel 
section 14 of a ski boot via two element contact pins 16 which extend 
through a semi-rigid phenolic support 18 into and through apertures 20 in 
heating element 12, where the ends thereof are upset to permanently secure 
the pins to the heating element. As can be seen in both FIGS. 1 and 3, 
pins 16 are slotted to provide resilience when laterally compressed, and 
extend through boot section 14 into contact apertures 22 in boot anchor 
24, which is secured to boot section 14 by two screws 26 extending 
inwardly through anchor apertures 28 boot section 14 to engage "T" nuts 
30. Contact pins 16 are laterally compressed by sleeve-like anchor contact 
posts 32 surrounding pins 16 where they extend through contact apertures 
22, contact pins 16 being frictionally but removably secured in anchor 
contact posts 32 by the aforementioned lateral resiliency imparted by the 
diametrical slots. Anchor contact posts 32 may be adhesively bonded or 
mechanically secured by interference fit to boot anchor 24. 
As can be seen in FIG. 3 of the drawings, the sliding frictional engagement 
of contact pins 16 in anchor contact posts 32 permits the boot assembly 10 
of the present invention to be installed on any standard ski boot whether 
the boot wall is merely a thin plastic shell or is a heavy laminate. The 
frictional contact also permits the boot liner or bladder to which heating 
element 12 is affixed to be easily removed from the outer boot for drying 
after wear or for installation or removal of custom-fit prosthetic devices 
such as arch supports, heel lifts, etc. 
FIGS. 2 and 4 of the drawings show a first preferred embodiment of the 
power pack assembly 38 of the present invention. Assembly 38 comprises a 
battery case 40, including two mirror image battery case halves 42 and 
42', which encase two sub "C" cell Ni-Cad rechargeable batteries 44. 
Batteries 44 are electrically connected in series by battery shunt 46, and 
electrical connection to anchor contact posts is provided by two 
mirror-image battery spring contacts 48 and 48', which are fixedly mounted 
in and to plastic contact housing 50, which in turn is secured to case 40. 
Wave spring washer 52 surrounds contact housing 50 inside of battery case 
40. Elastomeric water seal 54 is bonded to the bottom of battery case 40 
and surrounds the boot anchor receptacle aperture 56 extending into the 
interior of the battery case 40. The battery case halves and the contact 
housing may be adhesively or mechanically secured together into an 
assembly, as well known in the art. 
A more complete appreciation of the sophisticated simplicity and the 
advantages of the present invention over the prior art will be afforded 
through reference to the components of the invention. FIG. 5 shows boot 
anchor 24 from the top, as it would appear when mounted on a ski boot 
heel. Referring to FIGS. 5, 5A, 5B and 6, boot anchor 24 includes a 
laterally extending flange 60 of square configuration, surmounted by a 
truncated tubular anchor element 62 having lugs, tabs or flanges 64, 66 
and 68 extending laterally therefrom at its top periphery. Lug 64 defines 
a larger arc than lugs 66 and 68, both of which extend farther from the 
periphery of element 62 than lug 64. Lug 68 is placed symmetrically 
diametrically opposite lug 64, and lugs 66 flank lug 68 symmetrically to 
either side. The lower surface of lug 68 (see FIG. 6) includes a detent 70 
having tapering side surfaces. The interior of boot anchor 24 includes 
contact apertures 22 (to accommodate contact posts 32) which extend at 
their upper ends into the wall of element 62, and anchor apertures 28, 
which have at their outer ends chamfers 72 to accommodate the heads of 
screws 26 where anchor 24 is secured to a ski boot. Struts 74 under flange 
60 support flange 60 against forces exerted when power pack assembly is 
being attached to boot anchor 24, and generally lend rigidity to boot 
anchor 24. 
Referring to FIGS. 7 and 7A-7D, contact housing 50 comprises a cup-shaped 
plastic molding having symmetrically placed laterally cut slits 76 in the 
outer walls thereof, a diametrically extending full-height central wall 
78, a short lateral wall 80, two tubular spring towers 82 symmetrically 
flanking central wall 78, and a tubular end tower 84 at the end of central 
wall 78. Spring towers (see FIG. 7C) are cut out at their inner 
peripheries. The top edge 88 of contact housing 50 includes a tongue 90 
(see FIG. 7D) and an alignment post 92. 
Spring contact 48 is depicted in FIGS. 8A and 8B, as well as being shown 
from a third perspective in FIGS. 2, 4 and 12. Spring contact 48, and its 
mirror-image twin, contact 48', are preferably of nickel-coated spring 
steel, such as music wire. Small arc 94 provides lateral resiliency to 
large arc 96 which extends through the slit 76 of contact housing 50 to 
provide selective electrical contact with posts 32. Inner leg 98 of 
contact 48 rests in a tower cutout in contact housing 50 and provides 
torsional stability to the large arc loop 100. Vertical leg 102, extending 
perpendicularly to the plane of large arc loop 100, extends through an 
aperture in the battery case to the battery cavity, and outer leg 104 
leads to battery contact flat 106. 
FIGS. 9-11 depict one-half 42 of battery case 40, it being understood and 
appreciated that mirror-image half 42' is of like, mating construction, 
the dividing line between the case halves symmetrically defining anchor 
receptacle aperture 56. Case half 42 is of high-impact plastic, and 
defines one-half of a battery cavity 108 and an anchor receptacle 110. 
Partition wall 112 extends from floor 114 in the center of battery cavity 
108 and assists with case rigidity and proper alignment of spring contacts 
48 and 48' (see FIG. 4). Spring alignment struts 116 center wave spring 52 
in anchor receptacle 110 where case 40 is assembled (see FIG. 12). The 
bottom 120 of case half 42 defines one-half of anchor receptacle aperture 
56, which includes slots 64', 66' and 68' of similar orientation and 
configuration to boot anchor lugs 64, 66 and 68. Due to the symmetry of 
case half 42, one-half of slots 64' and 68' are present in case half 42, 
the other half in case half 42'. One each of slots 66' is located in the 
bottom of each case half. Similarly, a locking recess 122 is located in 
case half 42 and another in case half 42', while each case half defines 
one-half of switching recess 124. Locking recesses 122 are diametrically 
opposed in assembled case 40, and switching recess is located 
perpendicularly to a diametrical line extending between locking recesses 
122. Half-circular contact housing recess 126 is located centrally on the 
bottom of case floor 114, the other half being located in case 42', the 
two defining a circle and an alignment post aperture 128 (half of it shown 
in FIG. 10) so that contact housing 50, when inserted into case 40 with 
spring contacts 48 and 48', will be properly rotationally aligned when 
alignment post 92 mates with aperture 128. Spring contact aperture halves 
130, to permit the spring contacts 48 and 48' to extend from below to 
above floor 114 into battery cavity 108 (see FIG. 4) are located adjacent 
to and on either side of partition wall 112. 
FIG. 12 shows various elements of power pack assembly 38 superimposed to 
better illustrate the alignment and relative dimensions of the various 
parts of the assembly. It is not an actual section, nor is it intended to 
be taken as such. 
FIGS. 13, 14 and 14A depict a preferred embodiment of the heating element 
12 of the present invention. The flexible resistance circuit 140 of 
element 12 is printed on plastic substrate 142. Substrate 142 is 
sandwiched between single-sided adhesive tape 144 on the bottom, and a 
fabric 146 affixed with pressure sensitive adhesive on the top. Fabric 146 
also extends over support 18 and around contact pins 16. Tape 144 extends 
over the upset ends of pins 16, which hold pins 16 to circuit 140 and to 
support 18. Each pin 16 is in electrical communication with a circuit path 
148, which extends to a resistance circuit grid (not shown) at the 
opposite end of circuit 140. This half-oval shaped grid, the location of 
which is designated at 150, is coated with a pressure sensitive adhesive 
152 on its top. It should be noted that tape 144 stops short of grid 150. 
Finger tab 154 (FIG. 13), which is used to insert and pull out pins 16 
from anchor contact posts 32, is formed by the adherence of wings 156 of 
fabric 146 to each other after folding around the laminate of tape 144 and 
substrate 142. As shown schematically in FIG. 15, the heating element grid 
150 is adhered by adhesive 152 to the top 158 of a ski boot insole 160. 
The rest of the flexible circuit 140 on substrate 142 extends over the toe 
of the insole 160, along the bottom 162 thereof, and exits boot inner 
shell or bladder 164 (also referred to as a "bootie") through slit 166, 
running along the level 168 of bladder 164 to the point at which pins 16 
can be inserted into the contact posts 32 of ski boot 14 (not shown in 
FIG. 15). Spacing between the aforementioned elements in FIG. 15 has been 
greatly exaggerated for clarity in understanding specific locational 
relationships. 
Referring now to all of the drawing figures, but particularly FIGS. 3, 4 
and 12, the operation of the present invention will be described. Boot 
assembly 10 is installed, as previously discussed, on any pair of ski 
boots 14 of choice. Heating element 12 has been installed on the insoles 
160 of the boots 14, and run inside of bladders 164 as shown in FIG. 15, 
bladders 164 then being installed in normal fashion in boots 14 and pins 
16 inserted and frictionally held in anchor contact posts 32 of boot 
anchor 24. Power pack assembly 38 with fully charged batteries 44 is 
placed with aperture 56 facing boot anchor 24 at the heel of each boot 14. 
Slots 64', 66' and 68' on case 40 are aligned with lugs 64, 66 and 68 on 
boot anchor 24. Case 40 is placed over boot anchor element 62, which 
compresses wave spring 52 inside cavity 110. Case 40 is then turned 
90.degree. in either direction, which results in detent 70 on anchor lug 
68 engaging one of two locking recesses 122 on the inside of case 40 and, 
with wave spring 52, locking power pack assembly 38 to boot anchor 24. The 
heater remains inactive at this point, because spring contacts 48 and 48' 
are not contacting anchor contact posts 32 on the inside of anchor 24. 
Further 90.degree. rotation in the same direction as the initial rotation 
results in detent 70 engaging switching recess 124, and case 40 remains 
locked to anchor 24. The electrical circuit between batteries 44 and 
heating element 12 is now completed through contact pins 16, contact posts 
32 and spring contacts 48 and 48', as the latter have been rotated into a 
position when they biasingly engage the sides of contact posts 42. Wave 
spring 52 provides sufficient resilience to lock case 40 to anchor 24 in 
either the locking or switching positions of power pack assembly 38, and 
water seal 54 compressively engages flange 60 on anchor 24 to form a 
water-tight seal between flange 60 and the bottom of case 40, thus 
isolating the electrical connection and switching function between boot 
assembly 10 and power pack assembly 38 from water, ice and snow. When it 
is desired to turn off the heat, 90.degree. rotation of case 40 will 
achieve that result, and further 90.degree. rotation in the same direction 
can be used to remove power pack assembly just prior to a race, or to 
replace it with a fresh assembly, or to recharge batteries 44 at the end 
of the day. 
Referring now to FIGS. 16-30 of the drawings, the elements of a second 
preferred embodiment of the invention will be described in detail. It 
should be understood that the elements of the second preferred embodiment 
differ primarily in structural simplicity, and that the 
heretofore-described method of operation of the first preferred embodiment 
is also applicable to the second. 
The elements of an alternative preferred boot assembly 210 of the present 
invention are depicted in FIGS. 15, 23-25A and 28-30. Heating element 212 
(see FIG. 15) is similar to heating element 12, except that the flexible 
circuit substrate terminates under the arch of the insole inside the 
bootie, bladder, or inner shell 164, whereupon the electrical circuit 
extends to the heel of the boot 14 via two twenty-two gauge wires 400, 
which extend through small apertures in the side or bottom of the bootie, 
bladder or inner shell 164 and run along the outside thereof. It has been 
found that the foregoing structure facilitates placement and retention of 
the heater element in the boot, as well as removal and re-insertion of the 
bootie, bladder or inner shell 164 with the heating element in place. 
Wires 400 may be soldered to contact pins 216 (FIG. 30) in addition to 
being mechanically clamped thereto by the upsetting of the ends thereof 
after extension through plenolic support 18, in the manner shown in FIG. 
14A with respect to element 12 and pin 16. 
However, it is actually preferred that pins 216 not be connected by support 
18 in some instances, as certain brands of ski boots include ribbing on 
the interior of the boot shell and it is easier to extend the pins 216 
between the ribs into posts 232 when pins 216 are not linked together or 
interconnected in a single assembly. 
Pins 216 are not slotted or bifurcated as pins 16, and are frictionally 
maintained in anchor contact posts 232 (FIGS. 28, 29) by resilient inner 
fingers 233. The outer surface of posts 232 may be knurled as shown at 
235, to facilitate an interference fit retention of posts 232 in contact 
apertures 222 of boot anchor 224, but this has been found to be 
unnecessary. 
Boot anchor 224 (FIGS. 23-25A) is similar to boot anchor 24, and is secured 
to a ski boot 14 by two screws (not shown) similar to screws 26, but 
having a thread design adapted to engage the inner walls of anchor 
apertures 228 so that nuts, such as nuts 30, are unnecessary. Such screw 
designs are well known in the art and are not material to the present 
invention. Boot anchor 224 includes a truncated tubular anchor element 262 
having lugs, tabs or flanges 264, 266 and 268 extending laterally 
therefrom at its top periphery, and the shape and placement thereof on 
anchor element 262 is virtually identical to the lug configuration of boot 
anchor 24, with the exception that there is no detent on the bottom of lug 
268. Contact apertures 222, into which are inserted anchor contact posts 
232, extend at their upper ends into the wall of element 262. 
Referring to FIGS. 16-22, 26 and 27, an alternative preferred embodiment of 
power pack assembly 238 comprises a battery case 240, including a battery 
housing cover 242 and a battery housing base 244. Contact housing 250, a 
plastic molding like battery housing cover 242 and base 244, is sandwiched 
therebetween when case 240 is assembled, and provides a floor 314 for 
batteries placed inside battery cavity 308 of cover 242. Ni-Cad sub "C" 
cells 44 are deployed in battery cavity 308. Partition buttresses 402 and 
side buttresses 404 inside cover 242 provide rigidity to cover 242. 
Batteries 44 are supported by floor 314 of contact housing 250, and are 
positioned by cradles 408 (see FIG. 17C) and end stops 410. Alignment of 
contact housing 250 inside battery housing cover 242 is facilitated by the 
mating of alignment post 406 in alignment slot 412, contact housing 250 
then being disposed in recess 414 against side buttresses 404 and 
buttresses 402. Spring contacts 248 and 248' are, like their counterparts 
48 and 48', mirror images of one another, but are much simpler, comprising 
(FIGS. 26 and 27) contact loops 416 and leg 418. As shown in FIGS. 17, 
17B, 17C and 18, contact loops 418 lie in arcuate channels 420 in contact 
housing tower 422 of contact housing 250, extending laterally beyond the 
diameter of tower 422 through windows 424. Channels 420 surround contact 
housing posts 426 and, when spring contacts 248 and 248' are disposed in 
channels 420, plastic caps 430 and 430' (FIGS. 20-22) are snapped over 
truncated posts 426 to maintain spring contacts 248 and 248' in place. 
Caps 430 and 430' are mirror images of one another, each having an edge 
432 of enlarged radius to match that of tower 422, a tab 434 to align with 
dimples 436 off of channels 420 in towers 422, and a cutout 438 to align 
with ejector pin apertures 440 in tower 422. 
Legs 418 of spring contacts 248 and 248' extend through frustoconical 
contact passages 442 when contact loops 416 are in channels 420, and are 
bent to reach the ends of Ni-Cad cells 44 (FIG. 17C), where they are 
soldered at 444 to the contacts thereof. As with the first preferred 
embodiment of the invention, the other ends of cells 44 are laterally 
electrically connected via a shunt 46 (not shown). 
Battery housing base 244 is a single-piece plastic molding and defines, 
when assembled with contact housing 250 and cover 242, an anchor 
receptacle 310, into which opens anchor aperture 256, of similar 
configuration to aperture 56 of the first preferred embodiment. Aperture 
256 includes slots 264', 266' and 268', of similar orientation and 
configuration to boot anchor lugs 264, 266 and 268. Spring alignment 
struts 316, like struts 116, serve to centrally align wave spring 52 about 
aperture 256. In lieu of the locking and switching recesses used in the 
first embodiment, discontinuous arcuate track 450 is utilized for locking 
and switching of the power pack assembly 238. Gaps 452 in track 450 
provide an initial secondary locking position for the power pack assembly, 
while locking gaps 454 serve the same purpose as locking recesses 122 in 
the first preferred embodiment, and switching gap 456 performs the same 
function as switching recess 124. As can be seen in FIG. 19A, track 450 is 
of reduced height at segments 458 bounding switching gap 456, to give a 
different feel when the power pack assembly 238 is rotated from a locked 
position with lug 268 in one of locking gaps 454 into switching gap 456 to 
turn on heating element 212, than when power pack assembly is being 
rotated in the opposite direction to remove it from boot anchor 224, thus 
signalling the boot wearer of the proper direction in which to rotate. 
Other than the inclusion of auxiliary or secondary locking gaps 452 to 
provide additional security for power pack assembly 238 in the event of 
impact, skier falls, or other shocks and jars, the insertion and rotation 
of power pack assembly 238 into boot anchor 224 is identical as far as 
operation of the device is concerned. Water seal 54 and flange 60 or boot 
anchor 24 have been eliminated in the second preferred embodiment, and in 
lieu thereof a Lexan or other resilient donut or washer is placed between 
wave spring 52 and anchor aperture 256, the donut being flexible enough to 
bend away from lugs 264, 266 and 268 when they enter cavity 310, and to 
fairly closely engage the outside side of anchor element 262 below the 
lugs to exclude ice, snow and water from the cavity 310. 
It will be appreciated by those of ordinary skill in the art that the 
present invention comprises a novel and unobvious solution to a 
long-recognized problem unsolved by the prior art. The present invention 
provides a universal ski boot heating system adaptable to any boot make, 
design, or last, and one that does not hinder or impair normal boot 
function and maintenance. Moreover, the present invention reliably 
functions in all weather conditions, and is rugged enough to survive the 
demands placed upon it by the most aggressive skier. Further, the easy 
replaceability of the present invention's power pack assembly permits the 
carrying of spare power packs for long days on the slopes, or removing the 
power packs when skiing and replacing them when waiting for lifts. The 
present invention also permits ski racers to maintain foot warmth until 
immediately prior to a race heat, and then remove the power packs to be 
free of the excess weight during the race. 
While the present invention has been described in terms of a preferred 
embodiment, it is not so limited. Many additions, deletions and 
modifications may be made to the preferred embodiment without departing 
from the spirit and scope of the claimed invention. For example, a 
non-rechargeable power source may be used; the anchor and anchor 
receptacle locations might be interchanged between the boot assembly and 
power pack assembly; other designs of resilient contacts are usable; and 
more.