CA2100471A1

CA2100471A1 - Self-regulating tire pressure system and method

Info

Publication number: CA2100471A1
Application number: CA 2100471
Authority: CA
Inventors: Ross D. Olney; John W. Reeds
Original assignee: Individual
Current assignee: Raytheon Co
Priority date: 1991-11-18
Filing date: 1992-09-11
Publication date: 1993-05-19
Also published as: WO1993009964A1; US5411051A; IL103719A0; US5293919A; JPH06501666A; KR930703159A; EP0566734A1; US5413159A; MX9206649A

Abstract

SELF-REGULATING TIRE PRESSURE SYSTEM AND METHOD
ABSTRACT OF THE DISCLOSURE
A self-regulating tire pressure system and method em-ploys a bistable valve (10) that allows air from a high pressure reservoir (6) to replenish the pressure within a tire (4) when it has fallen below an actuating pressure, and discontinues its operation only after the tire pressure has increased to a closing pressure that is greater than the actuating pressure. The system is capable of sensing the valve's (10) frequency of operation as an indication of a slow tire leak when the frequency exceeds a predetermined threshold, of sensing the number of valve (10) operations and the duration of each operation as an indication of a flat tire condition when the number of operations for a predetermined duration exceeds a second threshold, and of sensing the duration of the valve's (10) operation as an indication of a low reservoir (6) pressure condition when that duration exceeds a third threshold. The valve (10) includes a bistable diaphragm (94, 120) that receives a reference pressure on one side and the tire pressure on its opposite side, and snaps between two stable positions re-spectively opening and closing the valve (10) in response to the tire pressure falling below the actuating pressure and then increasing to the closing pressure.

Description

21~7~

8~L~ G~La~I~G S~ ES~ S~K AX~ ~T~OD

~AC~GROU~D ~ TE~_IEY~E~IQY

T~ n~ntion rel~t~s to s~ regulating pressure ~yste~s and ~ethods for vehicle tir~s, and more p~rticular-ly to ~elf-regulating ~y~te~s and ~ethod~ in vhich the tir~
is automatically repleni~d fro~ ~ high pre~sure reservoir in response to a ~ensed low pre~sure condition in the t~re.

De~cri~tion of tbç Rel~ted Ar~
Low tire pressure i5 an lmportant cause of excessive fuel consu~ption, tire we~r and impaired steerability. A
normal tire ~ill typically leak on the order o~ 25 percent of its pressure per year due to its inherent per~eability, It is t~us good practice to check tire pressure on a regu-lar basi~. ~owever, even checking tire pressure every few week~ ~ay not prevent these adverse a~ects ~hen a ~low lea~ is pre ent, and the 1~ ~ay ~o undetected unle~ a careful record i~ m~int~in~d o~ ho~ fr~quently the pr~surQ
~n e~ch ~ir~ ha~ to ~a replen~sh~d. A fa5t leak or ~l~t cond~t~on c~n rapidly c~u~ ~a~agQ to th~ tire an~ n render it unusable in a short period o~ time, but this con-dition ~ay go unnoticed by an inexperienced driver until it : i~ too late.
It $~ thu~ ~ighly desirable to ha~e 50~e ~ech~ni th~t ~uto~tically replenis~ the tire pre~sur~ ~hen i~ i~
too low, and t~at warns ~o dr~v~r o~ the lo~ pressure con-dition. One uch systo~ ls dl-clo~ed in U.S. Yatent No.

` ~ 2 21~7~

4,067,376 to Barabino This patent incorporates a high pressure reservoir into the vehicle wheel, and uses a valve t~at automatically opens a passagew~y between the high pres-ur- reservoir and the tir- in r-sponsQ to the tire pressurs ~alling below ~ sel~cted thre5hold l-vel Oper~-tion of the valve al~o caus-- a onic or ultra50nic ~ign~l to be q-nerat d which ~ d~tected by a ensor nount~d ln close proxinity to thc wheel, typic~lly within the wheel vell When it senses a v~lve operation, the sensor init~-ates a visual and ~udio warning for the driv-r To differ-entiate between the different tires, the ~alv- on each tlre ~ay be tuned to g-nerat- a ignal vith a unique frequency, or the sensors for the diff-rent tires ~ay be tuned to de-; tect difrerent component~ of ~ unifor~ v~lve ig~al Another system is di~closed in U S P&t-nt No 4,742, 857 to Gandhi In tbis patent the tire valve includes a magn-t that moves in response to a fallinq tire pressure Novement of ~he magnet to a low pressure position is sensed by a solenoid mounted on the shock absorber adjacent the tire The magnetic field from the moveable ~agnet inter-cepts the sol-noid at each tire revolution, g~nerating a voltage in the solenoid that varies with the magnet's posi-tion When the magnet'~ sensed position indicates ~ low pressure condition, a ~arning i8 provided to the vehicl-operator ~f the op-r~tor wishes to repl~nish the t~r-pressur-, he or she actuates a cwitch that supplies current to t~ solenoid for t~e appropriate tire The ~olenoid produces a ~gnetic fi-ld that nove~ lt- a5soci~ted magnet to a position at which a valve from a high pressure reser-voir within the wheel i~ opened so that air can flow intothe t~re Whil~ the ~bove y~t~cs can effectively replenish the air pres~ure ~ithin a tire, they are incap~ble of distin-guishing between nornal long term leakage rrO~ a tire, a ~lcw le~k condition that requires rep~ir, and a fast leak :.

- - . 210~i~7~

:
or flat tire condition The vehicle operator is thus unin-; formed a~ to w~ether a tire repair or replacement is called for The operator is also not supplied with any informa-tion as to the cond~tion of the high pressure reservoir, S and whethQr it requir-s replenishnent Furthermore, the prior uc- of eparate tranc~itt-r~ within each wheel and a~oclat-d receiver~ on th v hicle re~uires a power source within each w~eel and complex l-ctronics, and is unduly expenslve.
an after narkct sensor for lov tire pressure ~as been uark t-d by Epic Technologi-s ~nc The sensor ~onitors tir prec-ure and cau~-~ a radio frequency (RF) ignal to be tranc~itt-d in cas- the pr-~-ur- falls below a predeter-~inea ~et point tran~ ion of the RF ignal actuat6~ a ~5 warning for the ~e~icl- driver Ho~e~er, the system doe~
not hav- any nechanis~ to autonatically replenish the low tire pressure t SUMMARY OF THE INVENTION
The present invention see~s to provide a new self-reg-ulating tire pressure syJtem and ~ethod that senses a low pressure condition vithin a tire, automatically replenishe~
the pressure to a desiredl le~el, is less complex and expen-~i~e than prior approache~, provide5 the ~ehicle operator vith ln~ornation on the cause of the 1~ pressure condition ~nd ~ th r ~ir repair or r-plweoent i~ required, ~na doQs not require th~ int-rv~ntion of the vehicle operator to re~tor tir pre~ur-These qoals are accomplished with the use of a bi-ctable valve that openc an air flow between the high pres-~ure r--Rrvoir and the tir- when the tire pressure f~llc below ~ predeternined ~ctuat~ng level, and halts th¢ a~r flow when t~ tire pres~ure has increased to a clocing pre~sure that i5 gre~ter tb~n its actuating pressure $he val~e condition i~ co~munic~t~d to t~e vehicle by ~e~n~ of ~.

21~71 a primary winding on the vehicle cbassis ad;acent the wheel, and a second~ry vindlng on the wheel that is con-nected slong with a 5et of val~e contacts in a secondary circuit The valvc contact~ open and close as the valve - S switches betw en its t~o tabl- po-$tions, produc$ng a cha~ng in t~ i p~danc of th econdary c$rcuit that $-r fl-ct-d back to t~- pri-~ry winding Th- r-fl-ct-d in-pedanc- provide an indication o~ the ~alv- operations ; a logic circuit ~uppli d by tb~ pri~ary winding dlr-f~r ntiate~ betveen ~ariou- lov pre--ur tire condition~
If tb- frequ-ncy of valv- operation xce~ds a predeter~ined thr -hold, a ~lo~ l-a~ a~ oppo- d to a nor~al pres~ur~ los~
throug~ the tire wall i- indieat-d Wh-n the duration or th- valv- operation xc--ds a pr d t-r~in d thre~hold, a low r-s-r~oir air pr---ur- eonditlon i~ indicated When the nuik r o~ valve operat$on~ that last for a pr-d~ter-~ined duration exce-ds a predeter~in~d threshold, a flat tire ~it~ation is indicated The valve preferably incorporates a bistable diaphrag~
that ~oves between two stable positions respectively open-ing and closing the air flow passageway from the h$gh pres-sure r-~ervoir In on- e~bodin nt the d$aphrago conprises a flexible nembrane t~at carr$es a r$rSt ~agnetic ne~ber aligned w$th a ~tat$onary ~agn-tic ~e~ber At least on- of ~ 25 th- nagn-tic neiber~ i~ nagn-tiz~d to hold the two nQ~bor~
tog-ther ~ith the diaphragn clo~ing the air flow p~ssag-way fro~ th ~gh pre~ure re~ervoir when t~e t~re pres~ure xceeds the ~ clo~ing pre~-ur-; the diap~ragn ~lex away from t~e second ~agnetic ~ember to its other ~table position and opens the air flow passagew~y when the tire ; pressure ~all~ below the valve actuating pres~ure ln a econd ~bodiment th- bi~tabl- diaphrag~ i~ a pre~tressed metal diaphrago that i- oriented about a centr~l plane and has stabl- po~itions on oppo~it~ ~idQ- o~ th~t plane The ~ 35 ~ tA~ phr-g- ~Ay b lodg-d ln a r-ces- th-t allcw- A r--':, .;' ' .

-` 21~0~7~

stricted movement of the diaphragm ~hen it moves between its bistable positions, thus enhancing the diaphragm~s snap action In this embodi~ent an air impermeable flexi~le diaphrag~ may be connect-d to move with the ~etal dia-s phrag~, and spans the bousing in whlc~ the recess is for~edto block tb- flow of air therethrough - 5b- valve co~par - th tir pressure vitb a reference ~ pr~s~ur- th~t can be provided tron sources such as a pres-- ~ur regulator, a pring or ~-al~d bello~s A ~lov of air fron the higb pres~ur r ~-rvoir to tbe tire is actuat-~ ed when tb- differential betw en the compared pressure~
i exce-d~ a tbresbold anount Furtber features and advantages of the invention vill be appar-nt to tbose kill d ln the art from t~e folloving d~tail-d dcscription, t~k n together with the accompanying dr~wings, in which:

DESCRIPTION OF TH_ DRAWINGS
FIG 1 is a sectional view of a portion of a vehicle tire and wheel illustrating the basic mechanical elements ~; of one e bodinent o~ the lnvention;
; FIC 2 is a block diagr~o of th- invontion;
FIG 3 is a diagra~ of a t$re and ~heel illustrating their int-rconn-ction through the bi-table valve used in t~- invention;
rIG 4 is a block diagran shoving the co~unication b-twe n th vehicle and wheel to detect when the val~e ha~
operat d FIG S is a logic diagra~ o~ tbe logir circuitry used to distinguish between ~arious types of tire leak and low reservoir conditions;
FIG 6 i~ a qrapb conparing the pressure in the higb pres~ur- r-~ervoir vith the ti~e reguired to restore th-tir pressur when a pr-s~ure regulator is used to provide 35 a r f-r-nce pr-ssure ~or tlt- v~lve:

. ' :,.

.

6 21~71 FIG 7 is a sectional view of a bistable valve con-struction that employs a pr-ssure regulator FSG 8 is a sectional view of a bistable valve con-~truction that e ploys both a pressur regulator and a pring a- a co~bined reter nc- pre~ure ~ourc-;
FIG 9 i~ a -ctional vi-v of ~n alt-rnat- bistable valv con truction that enploy- A eal-d b~llow a~ a r f-er~nce pre~ure ~ourco;
rIC 10 i~ a graph co~parlng th- pr ~-ur- in t~e higb pre~uro r-~ervoir w~th th ti e roquir-d to re~tore th tiro pre~sure when ~ pr ~ur- regulator is not e~ployed;
and FSG 11 i~ a frag~ ntary -ctional viev of a valvo and hig~ pr-~ure res-rvoir incorporat d into a conventional lS wh-~l DETASLED DESCRIPTION OF THE ~NVENTION
R f-rring fir~t to FIG 1 the rolevant element~ of a vehicle wh el 2 with a tir- ~ -at-d thereon are illustrat-ZO od The whe-l 2 includes a built-ln high pressure reser-voir 6, with ~ valvc t-~ 8 xt-nding into th- reservoir ~o that it can be r~pl-niJh-d vith pres-urized air The ~y~-t u i~ pref rably do-ign-d to operat- with ~ reservoir pre~-ur~ of over 100 pa~, which i- co conly available at ; 2S ~oct ~llling ~tations; lSO p~i ia pref rrod A valv- 10 provide- an air passaqeway botwe~n th- hig~
pro~ur re-~rvoir 6 and the interior oS th tiro 4 ~n accordanc- vith the inv-ntion, th valv 10 ha- a bi~tabl-construction such that it open~ the passa~eway betwecn the high pr-~ure res-rvoir and tir~ when the tir- pressure ha~
dropp d b low a predeter inod threshold level allowing air fro~ th- r--ervoir to flow into the tir- and r-stor- it~
pres~ure Th- valv- do-~ not close ofS th- passageway un-t~l th- pr-~ur- ~ithin th tir- ~a8 reach~d an elevat d ; 3S lev-l th~t excoed~ th original actuating pres~ure For ' .~

`::

: ' , ~, 21~

exa~pl-, th- v~lve ~y auto~tlc~lly ~ctuat~ n thc t~r-pr--~uro f~ b-low bout ~, p~l, but not r---t untll th-tlr- pr--~ur- h~ r-~cb-d high-r l-vel ueb ~ 35 p-1 Sh- open~d/clo--d ~t-tu- o~ tho v~lv- 10 ~- co~unl-5 c~t-d to tl~- v-hlclo t~y ~ an- of ~ coll o~ ~rlr- 12 ln-~11~ on tt~o out-r porlptl ry o~ hoel .~ ~ot o~ con-t~ v~lv 10 op~ h n th v lv- 1~ ln on t~t- u~ c~o-o vb-n t~ ln ~ oth-r t~t-, ~n~
~r ¢o~n ct-d ln no tlu vlndlng 12 vla ~ ~lr or 10 ~lr a 1~.. m- ov-r~ $n~1n~ cl~cult 1~ o~n ~h n t~
valvo cont ct- ar- o~n, and clo -d vh~ eontact- ~r-clo-d.
Mountd on th- vhe-l v-ll 16 o~ th- ~-hlcl- ch~
approxiaat-ly on~-quart-r lnch ~ro~ tbo ~beel winding~ ~2 lS ~- ~ pr~-ry wlndlng coll lt th-t ~en6es th- r~fl-ct-d ln-p~anc~ Or tt~ cond~ry wlnd~ng clrc~lt 12, and t~us de-t~roin-d wh~tber the v~lve 10 i- op-n or clo~ed. $he prl-~ry ~nd econdary winding- 18 nd 12 pr~-rably conprl--0 turn~ of 20 g~uge nd 6 turn~ ~f 1'~ g~u~o olld copper ~agn~t ~ir-, respect'v-lY A pair o~ le~d wlres 20 provld~
tbe lnput to prl~ry winding 18, ~nd ~1BO coupl~ tllc re-~l-ct-d ~p-dance eignal tro~ the pr~ary wlnd~ng 1- to log~c circu~try de~cr~d h . S1J11er conn etlon- ar-` ~ ~d- to the pr~y vinding- ~blch co~nlc~t~ ~lth second-2S ~ ~ llng- on ~ct ~ ep-retd,y, o t~t eh- et~
of ~ech t~r- c~n ~e displ-yed to th- op-r-tor eep~rately.
F~C-. 2 and 3 hov ~ddltlonal a~cta o~ overall y~t-~. me r-c~nd~ry ~l~ndlng 12 ~ rbown connoct~ ~n ~r~c wltb p~ir of cwltch contacts 22 tl~at ~re oper~ted by 30 thc bi-ta~le valve ~0, wbilc the prlmar3r vlnding lt pro-~lde~ ~ aignal to the sys:-~ ' s control electronlcs 2~ to - ~ndicat~ the ~ lve~ stat~;5. She cont:ol electronics ~ense the fre~ en~y and dLr~tion o~ ~he valve operatl~ns, lnter-pret t~ da~a t~ ~e;er~,r.e the r.a~u-e ~c 2 lo~ press~:e ~5 co:~dition, a~sd ac~l;a~e :he veh.c!e dash~oard dls?~ ay 26 ~o , ~ . .
: . :
..

8 21~71 notify the ve~icle operator of t~e naturc of a proble~ with any of the tires, and t~e identity of the affected tire ~ he high pressure r-~ervoir 6 supplies a reference pres~ure ourc- 28 such a- a pr-~sur- r-gulator; ~ seal~d b llow~ or a pring ean al-o b u~-d to stabli~h t~e ref-r-nc pr -ur . $b r f-r nc pr--~ur- nourc- 28 nor~ally baa a ~ingl- -t point at vbid it tr~-- to ualntain pr---~urc Wlth th~ addition ot th- bi~ta~l- v~lv- 10, a ~econd and lower ct point d-teruin d by th valv i- added For xa~ple, a~uu ~hat for an auto obll- tlr it i8 de~ir~d to b-gin r pl-ni~hing th t$r pr ~uro wh n it drop~ bel w 3~ p~1, and to continu- incr a-ing tb tir pr---ur~ until it r-ach ~ 35 p-i In thi~ ~ituation th- r-f-rence pr-~-~ur- ~ourc 28 doc~ not b gin corr-ct~ng th- tir- inflation unt~l thc low r -t point ~34 p~ r ached At that ti~e tbe valv- is ~ct~at d and ~llow~ hig~ pressure air fro~ reservoir 6 to repl-ni~h tb~ tire pre9~ure ~ben the tire prc~ure h~s been re-tored back to its nor~ et point (~uch a- 35 p~i) th valv- conncction automatically clo~e~, thereby discontinuing turther filling of the tire Shc r-ferenc- pres~ur- provid d to the valv- for a 150 p-i high pre~ure r---rvoir 6 vay b- about 36 p i, for exa~pl-A block diagra~ of circuitry that i~ u$table tor in-dicating th~ valvc'- ~tatu~, and thu~ wheth r a leak in t~
tir i~ pr s-nt, i~ giv n in rlG 4 A lo~ duty cycl~
~v ~orn, pr fcr~bly vith a duty cycl- ~ub~tantially lc~
than S0%, i~ g-nerat-d by an o-cill~tor 30 The ~vefor-is pre~-rably g n rat-d a- ies of pulse~ at a rrequ~n-cy of a few 8z to ~bout 20 Hz for low power ~pplicat~ons, wit~ a pulse duration o~ about 20-25 ~croseconds Ihe pulse~ op r~te ~ circuit driv r 32, pref-r~bly i~ple~ent-d as ~ PNP d~rlington tran-i~tor Tbe output puls~ ~ro-driv~r 32 are f~d through th pri~ary vinding 18 on the vehicle cb~s~is, ~nd are coupled thereby to the secondary vinding 12 The i~pedance of the secondary circuit that includes secondary winding 12 is refl-cted back to tbe primary wind-ing 18 to pro~ide an indie~tion of whother the valve con-tact~ 22 are open or clos-d, and thus wh~th-r th- valve is S op~rating to r-~tore th tir- pr-~ur- or i~ qyiese-nt Th r fl-et-d irp dane- app ~r a- a ~11 load ~-n th~
cont wt~ ar- open, and a~ a hlgb load wh n tb- eontact~ ~r-elos d mi. can b- i pl- nt d ln ~ev~ral way~ On-nethod 1- to provid- con tant curr-nt pulc~- to th- pr~ry and look for a reduetion in ~econdary voltag- when th- con-tact~ ~re elosed Anoth r thod is to provide eonstant voltag pri ary puls-~ and loo~ rOr an iner-a-- in ~eond-ary eurrent a~ an indlcation of elos-d eontact~ A th~rd nethod i~ to eonn-et capacitor 34 in parall-l vit~ t~-econdary w$nding 12 and eont~ets 22 ~h capacitor 34 to-gether vith the induetanc ot econdary v~n~ing 12 for~s a tun d circuit tbat o~cillat-s at a r-~on~nt fr-gueney when the contacts 22 are open, but is short-eircuited vhen the ; contaet~ 22 are closed An open contaet condition, re-fleeting an operation of the valve, produees a ~ringing~ or resonant o~cillation wh-n the core of the pri~ary winding 18 ha~ b co~e saturat-d and th- input pul~e turn~ off The wavefor~ refl-ct-d bac~ to tbe pri~ary ~inding 18 d througb a el~ping eireuit 36 to a zero cros~ng 2S eo~parator circuit 38 Th corparator e~reuit respond~ to i ringing ~ignal by ~quaring up it~ edges ~nd presenting a ~erier of pu~ to a count r ~0, the op~ratlon of vhieh i~
nabl d vh n the o~cillator 30 i~ op-ratlng by ne~n~ of a latch circuit 42 fed fro~ t~e 05cillator The counter 40 function~ as a hard~are filter, requiring a fix-d number of pul~e~ fro- th comparator 38 before it produce~ an output rOr the prinary/~condary circuit~ ~nd drive ~ignal de~crib d above, five input pulse~ could be requir~d to produc- an output fro~ countcr 40 T~i~ output trigger~ a 3 one-~hot l~tch 44 that operate~ a driver ~6 to turn on a ~' .

, , .
. ' .

10 ~Q~

low tire pressure indicator such ~s light emitting diode 48 on t~e vehicle's display panel Tbe circuitry of FIG 4 imply indicates that the bi-- stable pres~ure valve has operat-d, without identifying the tire eondition that eau~ d th- valv~ op-ration A logie eireult that re~pond- to th- ignal r fl-et d fron thc ~e-ondary winting eireuit back to th- pri ary winding by di~-tinqui~h~nq ~ tw--n di~f r-nt low pr ~8ur eond~t~on- i~
~ ~hovn FIG S It utili~-- a elo~k 50 that g~n rat-~ pul~-~
- 10 at a de~ired rat-, ~ue~ ~ l H~ Th- ~tatur of th- bi-~t~bl- val~, a- indieat-d by th- ~mpedanc- r-fl-eted baek to pri~ary winding 18, i~ f d ~rou an input lin 51 into a two-bit eount r 52 that op rat-- by producing a Ql output OvQr output line S~ the ~ir~t tiu the ~alv opQratQ~, and lS bot~ Ql and Q2 outputs r--p ctiv-ly ov~r output lin~ 5 and S6 th- ~ccond ti~e the valve operate~
Th- output of clock 50 and th- Ql output o~ the two-bit counter 52 are connect d r~pectiv-ly to tho clock an~
enable inputs of a ti~ing circuit 58 Th- ti~ing circuit deter~in~ the time int-rval b~tw en two ~uccessive valve op~ration~ If thi- int-rval 1~ les~ than a pr~det-rmined thre~hold duration, a ~lov l ak a- oppo-ed to a nornal long tcr~ lo~ of tir~ pr-~ur 1~ indicat~d For exa~ple, the ti ing circuit 58 i~ ~hown l-pl~ nted a- ~n lB-bit counter whic~ produce~ an output after running for 262,1~4 ~ocond~, or approxi nt ly 3 d~y- ~th 18-~it counter i- f~bric~t-d by conn cting re~d~ly avail~bl- 14-bit ~nd 4-bit count-r~
~n ~er~e-) a Q ~igh) output i- produc-d by count~r 58 when it h~s counted up to it~ liuit 5h- Q2 output of 2-bit counter 52 $s connected to a l~tch 62 that operate~ ~ ~dow leak~ p 64 on the ~e~i-cle'~ da~hboard p~n l The Q output o~ the ti~ing circult counter S8 iu connected through ~n O~ gat~ 66 to reset ~oth of t~- count-r- 52 and S8; ~ ~anu~l counter reset ~ o provided through OR gat- 66 11 2~Q~71 $~- op-~t~on of eb~ FIG. 5 clreult ln produclng a ~lov l-~k varnlng will now b- d--crlbod A~BU~- ~lr-t tbat ~ lo~ loa~ resent, eau-ing ~ucce6slvQ Yalve lgn~l- to be g~n-r~t-d ~t ~nt-rv-l- o~ le~ th~n 3 d~y- $h~ t s valv- lgn-l e~u~-- 2-bit count-r S2 to n~blo tbe op~r~-tlon ol tl~ng elreu~t eount r S~, wbleh begln- to eount up 5b -eond valv- lgn l app--r b ~or- eount-r SS ~-rea¢b-d ~t~ llnlt ~hl~ -eond lgnal ~etl~at-~ ~otb t~
Ql nd Q2 outFut- of 2-bit eount-r S2, ~hleh ~pect~vely eontlnu- tb- nable~-nt of tl~lng e~reult count-r 5~ ~n~
provl~ an lnput to l~teh 62, e~u~ng tb- ~-lo~ la~p 6~ to lllunlnat-A--u- n-xt tb~t a ~-eond valvo op~r~tlon i~ not ~--tect~d ~rore tt~- tloing clrcult eounter S8 )~a~ r-ach~ ~t-l~t In thl- ~it~tion ~h~ Q2 lnput to latch 62 reDain-low wb~le t~- ti~ing circult count~r 5~ counts 11 the way up to lt~ lini~, preventlng th~ ~-low lea~ la~p 64 fro~
llghtln~ A Q output 1- produc-d by tlalng circult countor SB wh n lt ro~che6 lt- linit, cau-ing both th- counter 58 ~nd th~ 2-blt countcr 52 to r~ot Th- n-xt v~lve ~i~nal to be received wil~ thu- pp-ar as ~n initl~l ~lqnal th~t enabl-c ~ r -tart o~ the lo~ic clrcult operatlon, wlt~ tho ~low ~-~k~ l-np 64 continuinq to be held of~ unle~ an ; additlona~l valve 5ign~1 i- ub--qu-nt~y recoived before thQ
tlalng clrcu~t count-r S8 ha~ countcd out ~ hil- t~ circult de-cribcd thua far in conn-ct~on v~t~ rIG 5 ~a~ been re~err~d to a~ e ~-low l~ak~ circult, ~t ~o-- not d~tlngulsh botu en a loH l-ak nd ~a-t l-a~
; or flat tlr- situatlon a fa~t le~k can b- ~-tocte~ ~lth a sl~ r logic circult t~at u-es ~ low-r capac~ty tlalng clrcu~t counter, ~or ex~ple an 8-blt counter that ~igbts t l-ak~ indlc~tor ~or succesBlve vnl~ op-ratlon~ ln le-~ than ~ ~nute~ operatlon o~ th- ~a~t leak~ det~c-tlon clrcuit c~n be u~ed to lock out the ~slow le~k~ detec-tor lor ehat ti~e Altern~tely, t~e manual re~et input 68 .

- ~ ~2 2~ 71 to OR gat~ 66 c~n be u~-d to dlstingul6~ a ~a-t ~rom low le~k. lf the oper~tor ob~-rve6 th- ~-low leak" laap, h~ or ~h~ c~n o~erat- thc ~nu~l r--~t to xtlngul~ t~- la~p.
S~ lt co~ - on g~ln In a bort per~od o~ tl~ a-t l~a~
I- lndle~t-d.
8-v-r~l dlt~-r nt tl~- ~n4 ~gh pr---ur- r --rvolr con~ltlon- c n b- d-t-ct-d ~y ob--rvlng th- dur~tlon ot t~
valv~ op ~ tlon-, a ca~ b~llty t~ t 1~ provld-d by tb-~ra--nt bl-t bl- v lv ap~ro cb. So d t-r~ln- th dur~t~on ot v~ op r-tlonJ, count-r cucb a- ~-blt count~r 70 r-c~ clock z~gn-l ~ro~ ~h- 1 Hz cloc~ S0, and both nab~e and r---t Igna ro~ tbo va1v- Input ~ln- S1.
: 5~e confl~urat~on c~u--- th- count~r 70 to count up v~an .; bot~ clock and nabl- ~lgnals ar p~ nt, and to ~D~dl-~t~1y r---t when th- n-bl- ~gn~ re~o~ed. Count~r 70 d-t-ru~ne~ th~ ~urat~on o~ e-ch ~ - op-r~tion. ~t- -v-~ ntb ~nd lghth output blt-, r-cp-ctlv~1y Q7 ~nd Q8, ~r-`~ co~n~ct-d ~s Input- to AND qata~ 72 and 76, respect~ve1y.
~he va1ve aignal llne 51 1- conn-ct-d a~ ~ econd lnp~e to bot~ o~ eh~c- AND g~ees. Thu6, AND g~t- 72 v111 produc- an output vh-n tb- Q7 output of output of count-r 70 go-~ h~gb nd ~ v~v- ~gn-l ~c pr---nt, nd AND g-to 76 ~11 produ~
~n output w~on t~ Q8 output i- high nd the valv~ algna1 ~- t~11 p~-s-nt. Sn- Q~ nd Q- counter outputC corr--pond 2S eo ~-lv- op r~tlon- o~ 12~ nd 2S6 -condc, r--p-ct~v-ly.
: ~ r pr-sentatlv- rol-tlon~hlp b~tw~n th- alr pr---ura vlt~ln tho ~lgh pressuro ~ volt and th- dur-elon ot t~
:- v~lv op-r t~on, when ~ reg~l-te~ r-Serence prec~ure ix eo~pared ~it~ the ~ir- pr-s-ure to ~ctuete f10v of alr 30 ~r~ th¢ re~-rvoir to the tlre, 16 lllustrat-d in FIC. 6.
Slnc- a~r i~ blcd fron tb- bigb pre~re reeervoir durlng ~ch ~ l~e operat~on, lt~ ~reeeure vi11 progr~c~lv-1y de-cre~Se ~or nultip1e valve operatlon~, or ~ on~ va1v- op~r-tion l~-tS for ~n extend-d p-riod of ti~e. ~he reductlon in res-rvolr pres~ure as ~ function of the aqqreg2te ti~e . . .

.' ~

~' ~ 13 21~

the valve bas operated, either as a result of ~ultiple op-erations or from a single extended operation, is indicated by curve 78 The rate of pressure reduction in the reser-voir is a function of the initial reservoir pressure, the valve ~et point pres~ur -, and the relative volunes o thc res-rvoir and tire To provide th oparator with an indi-cat$on that the pre6sure within the r ~ervoir ha~ been re-duced to a point at which it ~hould be repl-ni~hed, a "res-ervoir low~ warning can be provided at a ~omewhat arbitrary selected pressure, such a~ 50 p~i Sn additlon, extend-d mobility tires are presently conte~plated t~at can continue to be operated for up to ~everal hundr~d nil~ ter a ~lat has been incurred a warning can also be provided if thi~
occur-These v~rious situations ~re indic~ted in FIG 6 When the reservoir reache~ an und-sirably low pressure, such as 50 psi, the ~alv- operating tine neces~ary to re-; plenish the tire pressure increases to T1 For a flat inan extended nobility tire the valve will repeatedly oper-` 20 ate, with the tire gradually losing pressure and the reser-voir being further depleted with each operation; the dura-tion of each operation will remain relatively constant at T2, until a pressure of about 1 psi is re~ched (when a 1 psi pressure differential i8 used to actuate the valvQ) Thereafter the valve ~ill re~ain open ~ith little or no furth~r replenish~ent of tire pressure ~eferring back to FIG 5, a ~reservoir loY~ ~ituation i~ di~played by a la~p 78 that i~ actuated by a latch 80 when both the Q7 and the valve signals are presented to AND
; 30 gate 72 To display a flat tire warning, a 3-bit counter 82 connected to the Q7 output of 8-bit counter 70 produce~
an outp~t when counter 70 has counted up to Q7 ~128 sec-onds) eight separate times This corresponds to eight valve operat$ons of durat$on Tl (FlG 6), $ndicating that the tire pressure has fallen to les~ than 20 p8i. The out-;~:
. "

, .-,, , . ' '' ~, ~ '' .

14 2 1~0 ~7 1 put of 3-bit counter 82 is delivered through an 0~ gate 88 to a latch 90 that lights a "flat tire" lamp 92. The flat t~re lamp 92 is also illuminated by a single occurrence of the Q8 (256 seconds) output of counter 70, processed through AND gate 76 and OR gate 88. Even i~ the 3-bit counter 82 b~s not yet lit the ~l~t tire la~p 92, the oc-currence of a valve oper~tion for 256 second~ or ~ore can be taken as an indication of ~ fl~t tir~.
Only a few indicators that ~ay be obtained ~rom the information regarding valve operating frequency and oper~t-ing duration have been described. Numerous other warning indicators that t~ke ~dvantage of the bi~table v~ve e~-ploy-d by the invention may ~lso ~e envisione~. It should also be realized that the ~ssign~ent of spec~ic ti~es ~uc~
as 128, 256 or 512 seconds to ident~y particul~r ~itua-tions is somevhat arbitrary, and can be ad~usted a~ nQces-sary to meet the needs of any particular tire/wheel syste~.
One implementation of a suitable bistable valve 10 i~
; shown in FIG. 7. A flexible diaphragm 94 spans a compart-ment 96 within the valve housing, segregatins the pressure on one side of the diaphr~gm from that on t~e other side.
A permanent ~agnet 98 i~ affixed to a striker 99 clamped to ; the center of the diaphragm, and is 21igned with ~ bore 100 for~ed in a valve end piece 102 of ~agnetic naterial. A
regulated pressure of s~y 36 p8i i~ suppli~d fro~ a pres-sur~ regulator 103 to the end piece 102 through a condult 104. The pressure regulator 103 is supplied with air fro~
th- high pressure reservoir via a conduit 105, ~ith ~
~ranch conduit 106 supplying the same reservoir pressure to the opposite end of tbe valve housing. A valve stem 108 on th~ opposite cide of diaphragm 9~ fro~ the ~nd piece 102 receive~ the re ervoir pressure ro~ conduit 106 on one sid~, and on it~ ~pposite 8ide h~ ~n ~ctuating tip 110 that i~ al~gned witb th~ d~aphragffl str~ker 99 Yithin co~-partment 96. The c~part~ent 96 is vented to ~be tire '' , . . . : , :
.
- ~
, ` 15 21~Q~71 through an outlet 112, and i8 ~egregated from the reservoir pressure of conduit 106 by a flange 114 that retains th-valv- ~te~ 108 in place The diaphrag~ 94 thu~ receives the regulated pr-ssure S on it~ right hand ~id-, and th tir- pre--ur- on it- l-ft ~and aid m diaphrag , aagn t 98 and valv- end pi-c-102 r el ct d ~o that t~ nagn t r-~aln- eated as~in t th- nd pl-c- 102 for a tir pr~ur~ gr-ater than th-d-~ir d v lv- actuating pr --ur Thi- e-tablishe~ one Or th valv-'- two ~tabl- conditions When th- tir- pr s-ur fall~ b low th actuating thr Jhold, ay 34 psi, th- in-cr a~ d pr ~ur diff-r nti-l acro - th diapbrag~ cau--a lt to fl-Y and begin to lift th ~agn-t 98 avay fro~ th valv nd pl ce 102 Th nagn t'~ ~ove~ent avay fron t~e ;~ 15 v81v- end pi-c- in turn r duc-- t~ ~agn tic forc- of at-traction b tween th ~- two l-J-ne-, thu~ acceler~ti~g th-movement of the diaphrag~ to the l-ft A5 the diaphragn ; continue~ to travel to th l-ft, but before it read-s it center position, it push-- again~t the valve stem's actuat-ing tip 110, opening an air pa~sageway through tbe valve ~t~n that allows reservoir air from conduit 106 to flov through tbe valve ~te~ and outl-t 112 to the tire The valv~ ~t~ re~ain~ open unt$1 the tire pressure has in-~ cr a~ d to th- val~e'- -cond et point, for exa~pl- 3S
- 2S p-1 At th$~ point the pre~ ure differential acro~ the diaphra0 i~ r duc d to 1 p $, and the r-sidual ~agnetlc ;~ forc- b t~e-n the per~an-nt ~agn t 98 and the ~agnetic nd pi-c 102 cau~-~ th- diaphragn to lift off the actuating s t~p 110, ter~inating the flow of air into the tire Since th- diaphrag~ is now moving towards the end piece 102 t~
agn tic attraction betwe~n ~agnet 98 and tb~ end piec-incr a~e~, cau~ing th- diap~rag- to ~nap over to th- right ~-~ to a ~tabl- o~f po~ition with the ~agn~t clamped to the end ~;~ pi c- 102 Sh~ valv- 1- thu- truly bi~table, vith only two t ble ' . .
, ' . ' .

16 2 1~ 47 positions In one position t~e ~al~- is fully orf~ wit~
the ~gnct 98 clamp-d aga$n~t the end piece 102 In th-otb~r ~t ble position th valve ic ~ully open, wit~ the strik r 99 depres ing the valv- stem ~ctuating tip 110 Th- n~tallic nd pi c- 102 and t~ agn-t 98 for- th-contact- ~2 that were d wrib d in conn ction with FIG~ 2 and ~, and that are connt d in th condary circuit to indicat- vh th-r th- valv- i- op n or clo- d El-ctrical l-ad vlr - 116 and 118 ar conn-ctd r -p-ctiv-ly to th nd piec 102 and to th n talllc tri~ r 99 for thl~ pur-; po~- Wh~n the ~agnet 98 i- cl~mped again-t tAe end pi-ce 102 in tb- po-ition ~ho~n in FIC 7, th contact- ar-; clo~ed nd th capacitor 3~ of FIG ~ i~ ahort-circuited, thu~ pr~-nting a ringing in th secondary circuit and pro-lS ~iding n indication t~at th- valve i- of~ Wh n the dia-phragn ha- fl~x-d to the l-ft and $- depr-~-ing the valv-stQn actu~ting tip 110, th- ~agnet 98 i- el~ctrically i-o-lat d ~ron th~ end pi-ce 102; thi~ open5 the contacts 22 of FIC ~ and produces a r ~onant LC s-condary circu$t that ;~ 20 indicates the valve is operating It i- inportant that the valve hav- no 8tabl~ position other th~n fully open or fully clo-ed, so that it will not continuou~ly supply a ~nall ~teady air flow to a slow l~a~
~ithout cycling Anoth-r valv arrang~ nt th~t can also be u~ d for thi~ purpo-- i- illustrat~d ~n IG ~ S~veral ~le ~nt~ of thi- -bo~i~ nt ar~ the ~u e a- for th~ val~-ot nG 7, ~nd ar- id~nti~i-d by the a~e ref~rence nuoer-al~ Sn thç e~bodi~ nt o~ FIC 8 a pr-~tr ~s-d ~etal dia-phrag~ 120 has a peripheral lip 122 that 1~ cl~mped to the ~al~e hou~ing ~o that th- alaphrag~ 6pans the interior of the houaing an air i~per-e~ble fl-x~bl~ d~aphrag~ 12~
pan~ th hou~ing ad~ac nt to th ~etal diaphragn 120, with it~ p riphery cl~mped in plac~ ~o that a~r cannot flow fro~
on ~id~ of the rubb4r diaphr~g~ to th- other Th- tir~
- 35 pre~aur~ ~ introducçd into th- co~p~rt~ent 96 on the ~al~e ~, :' :
,, :. :

l?
.
~ide of th~ air impermeable diaphrag~ 124, while regulated pre~ure fro~ the pressur- rogulator (not shown) is intro-duced into a ~pring co~partnQnt 126 on the opposite side of ; th- netal diaphragm 120 through ~n inlet port 12?, and high S pr~ur air fro~ th r --rvolr i- introduc-d to a high pr-~ur ar ~ 128 at th- valv- inl-t a tallic conn~ctor 129 cla p- tb uiddl- ~-ctlon~ of th t~o dlaphrag~ and ~orce~ th ~ to flQx togeth-r An l-ctric~l connectlon 1~
n~d~ to th ~lv- st-o t~p 110 througb th v~lve ~te~ 108 via ~ tal collar 130 around th val~- ~t-u and a l-ad vir 131 that ext-nds t~rough a f--d-throu9h bushinq 132 ln th~ hou~ing ~all An lectrlcal conn ction 1- ~de to th n tal diaphrag 120 with a l-ad wire 134 th~t conn~ct~ to th~ v~lv housing at any con~ nient loc~tion ~ead ~$r 131 and 13~ are connect-d in -rie~ vitb the ~econd~ry ~in-d~ng on tb- vheel A coil ~prinq 136 i- lodg-d w$thin the ~prin~ co~part-~ent 126 betveen a lip on th- ~et~llic connoctor 129 and the oppo~ite end of the ~pring compart ent 126 ShQ spring 136 pro~ides a reference pr-ssure that opposes thQ tir-pr-~ura on the oppos$t- idc of the diaphrag~s 120 and 124 ~, to control th valve op ration While the ~pring 136 might ,~ b~ u d a~ the ~ole ~ource of ref-rence pr-~sure, th ; ~pring forc- t-nds be un~v nly di~tr~but~d acro~ t~e ~etal ; 2S diaphr~gn 120, ~nd tho ~agnitudQ of th pring torc~ vari-~
wit~ tb dl~phrag po~ition The~e dr~wb~cks are itigat-d `, with th- ~ddition of the r gulated ~$r prc~ure ~ithin th-~prlng ¢o4p~.t,~nt 126, which uppli-- ~n venly di~tribut-d pr-~-ur- to the diaphrag~ that does not vary with the di~phr~g~ position When th- regulated pressure is used toqeth r with the spring to provid- a reference pres~ur th~ pr~ng pr-~ure ~y be corresondingly reduced, such to about 20 p-i~
In th po~ition ~hown in FIG 8, the do~e of the pr -6tr ~-d ~et~l diaphr~g~ 120 i- flexed to the le~t te ~e-. ~

-:
. . . . .

- 18 2~ on~7 1 press t~e ~alve stem tip llo and actuate the valve stem.
High pressur- air t~us flow~ into t~e tire until the tire pr~s-ure has increased to the de~ired ~econd 5et point, at which ti~e the reduc~d pr ssure diff-rential across the S diaphrag- c~us~s ~t to nap to its -cond tabl- posit~on (indic~t-d by a dash-d lin ), with it- do~e fl-x~d to the r~ght avay fror th- ~al~- st u Tbe tvo load wir ~ 131 and 13~ ar el-ctr~cally conn-ct-d vh n the diaphr~g~ 120 i~
flex~d l-ftvard to actuat- th ~alv-, and l-ctrically s-p-~rated vb n tb~ diaphrag- i- fl x~d rig~tward to s~ut th-valve off The ~aking and br aking of th--- cont~ct~ pro-v~d-s ~n indicat~on o~ th ~alv tatus, in a ~anner ~ai-lar to (but out of phas- with) th con~act- ot FSG 7 $he prestr-ss-d ~ tal diaphra0 120 ha- only 2 ~tabl-position~, vith it5 do~- tl-x d ither l-ft or right a~ in-dic~t-d in rIG 8 Th- uetal diaphrag is pref-rably for~ed fro~ 0 005 ~nc~ thick tainle-- st-Ql, 1 25 inc~ ln di l t-r with a 0 04 ~nch high do~e Another valve mbodi~ nt that ~-ploy- a different source of reference pre~sur i~ illu6trated in FIG 9 In this ~bodirent a se~led b-llows 138 i~ f~lled to the de-- sir d r ~erenc- pressur-, uch as 36 psi A bl~table n~t~ldiaphragn 1~0 ~inil~r to th- diaphrag- 120 Or FIG 8 ha~
it~ cent-r connect d to uov- with th belloY~ 138 betwo-n valve actuating and v~lv- non-actuating po~itions A~
honn in F~C 9, the di~p~r~gn 1~0 ha- a c~ntral op-ning tb~t i~ noumed on ~ tri~ r 1~2 a~tl~ d to th- bello~-!" ~h-n fl-x t to th right a- hovn, th- val~ t~ 108 $-not ~ctuat-d When tb- tir- pre~sur- outs~de the bells~
drop~ belov thc valve actuating point, the reference pr~s ~ure wit~in the bellow6 c~u~e~ the diap~ragn to ~n~p to the l-ft, t pres~ing valv- ~ten t~p 110 to actu~t~ the ~lv~
Thi~ pernit~ bigh pre~sur re~ervoir air fro~ the le~t ~ide of the valve sten 108 to flow tbrough the valve ~nd out to th~ tire The po~ition of th- valve i~ ~onitored by the .
.. ~ ' ' .

-- 21 0047~

lead wire 131 connected to t~e val~e ste~ tip 1~0 as in FSG ~, and by a second lead wire 144 that is either con-nectQd to th- striker 142 through a ~etallic bellows end - plate 146, or through the -tallic diaphrag~ 140 in the valv- hous~ng it a good lectr$cal connection i- ~aintain~d batw -n tb -e tYo part~
Sh~ pr -tr -~-d tal diaphrag 1~0 1- ~inilar to th diaphrag~ 120 of FIG 8, but lt i- ~hown lodged within an inn r p riph-ral r c--- 148 tor# d in th- wall ot the val~e hou~ing ~he diaphrago thickn~ than tb- w$dth of the r ce~s, alloving th- diaphrag~ to ~float~ axially w$th-in t~ r-c -- ~hi~ add~ to th di~phra0'~ nap action ~hen it ~ov-~ tro- on- ot lt- tabl- position- to th- oth-r ; 1S a g n~raliz-~ curv that r lat-~ th- pre--ur~ in the high pr~s~ure res~rvoir to t~- valve operating ti~e r~-quir-d to replenish th- tir pre~sure, for a valv~ ~n which ~; a ~-al-d bellows or a spring but not a regulated pres~uro is u~-d a~ ~ reference for the tir- pressure, i- illustrat-ed in F~G 10 Since the pressure suppli-d by a sealed b~llows or cpring ref-rence will not fall b-low its prede-ter~ined ~-t point, even when the pressure in the higb pre~ure reser~oir fall- b low that ~-t point as ~ re~ult ot r p at-d val~ op ration, th val~- vill b- per~an~ntly actuat d onc- the high pr --ur re~ervoir falls to tb~
pr s ur t point tor r---tting th~ valv- att r an opera-tion lhl~ ndicated in F~G 10 kq a flatt-ning of the curva ~o that it beco ~- horl~ontal once th- illu~trati~
~t point of 35 psi is reached Even though the reservoir pr~s-ur- will fall below 35 p-i if the tir- continue~ to leak, th- reference pr~ur will renain at it~ pre~et l-v-~ ucb ~ 36 psi For thi- type of valv- th~ flat tire - warning logic of FIG S will not be applicable, ~lthiough th- oth r v~rning~ hown in FIG 5 can ~till be pro~ided FIG 11 show~ the valve of FIG 9 incorporate~ in~-o a ,, .~:

.
. .
: . .' ' ' : .

20 2~ f L

wh~-l 2. A ~ountlng lplnte 148 1- v-ld-~ ~c~oa- two ~ t~
eetlon~ o~ the wh~ol rla, vleh th~ o lS0 o rrl-~by th~ ~ountlng plae,~ wl~in ~ ~pace bet~n th- two ~h-ol 6ection~. Addltional plstes 152 ~nd 154 ~r~ ~ld-~ ~cro-~
5 contour~ aroun~l th~ perlphsry of th~ vh-ol to rOx~ r-a-r-~ro~ on~ t ~rQ lnt-rconn ct-d ~y ~ o~lnp lS6.. ~rhe ~!cond~ry wlndlnq 12 19 JhoyJ~ d ~lrou~ or 158, ~ proc~-lng oloctronlc~ td on ~ r-t-160 ln~lde a ~ol~od polyura ho~Jl7)g 162 . Sb~ lm n-10 tion CAn tl~u~ ~e inco~por~t~d lnto ~ et~ndArd vh~
though eu~to~ized wheelE~ ~lay also be provl~
A tir~ pressure reç~ulating ~y-t~ oQ~rating ~od that provides detailed information on the ax~ct condit1 on ot ttle tire, and is botl~ pl~ and inexpen~lve in con-lS ~tructlon, ls made po~ible wlt~ the lnvent~on. ~h~ ev-eral lllu~trious embod~ent~ of th- lnv-ntlon hav~ n ~hown and d~6cribed, numerous variations ~nd alternAt~ r-ent~ occur to tl~o~e ~kllled ln the art. For x-~mpl-, the valve~ de~crlb d b-r-ln ~rlll hav~ Applic~tlon~
20 OUt~ of tire pressure r~u~ation, ~nd the s~cond~ry v~n-~ing contact~ c~n be opera'ced nor~ally clo~-d r~ther ~han no~ally open. Such variations ~nd alternat~ Dbodl~nt~
~r~ contemplated, ~nd can be nade ~thout de~artlng Pro~
the ~plr~t ~nd l;cope o~ the invention as defined ln the 25 app-ndod clalD~.

Claims

WE CLAIM:

1. A self-regulating tire pressure system, compris-ing:
a wheel for seating a tire, said wheel including a reservoir for providing a high pressure air source, and a bistable valve establishing an air flow commun-ication between said reservoir and a tire seated on said wheel, said valve opening an air flow passageway between said reservoir and said tire in response to the air pres-sure within the tire falling below a predetermined actuat-ing pressure, and closing said air flow passageway in re-sponse to the air pressure within the tire increasing to a predetermined closing pressure which is greater than said actuating pressure.

2. The self-regulating tire pressure system of claim 1, said bistable valve including a reference pressure source and a bistable diaphragm for receiving said refer-ence and tire pressures on opposite sides of the diaphragm, said diaphragm having first and second stable positions respectively opening and closing said air flow passageway in response to said tire pressure respectively falling be-low said actuating pressure and increasing to said closing pressure.

3. The self-regulating tire pressure system of claim 2, said bistable diaphragm comprising a flexible membrane carrying a first magnetic member, said valve further com-prising a second magnetic member aligned with said first magnetic member, at least one of said magnetic members be-ing magnetized to hold said magnetic members together with said diaphragm in said second stable position when said tire pressure exceeds said closing pressure, and to allow said diaphragm to flex away from said second magnetic mem-ber to its first stable position in response to said tire pressure falling below said actuating pressure.

4. The self-regulating tire pressure system of claim 2, said bistable diaphragm comprising a prestressed dia-phragm oriented about a central plane and having stable positions on opposite sides of said central plane.

5. The self-regulating tire pressure system of claim 4, said reference pressure source comprising a sealed bel-lows with an internal pressure establishing said reference pressure, said sealed bellows bearing against said dia-phragm in opposition to said tire pressure.

6. The self-regulating tire pressure system of claim 4, said reference pressure source comprising a mechanical spring bearing against said diaphragm in opposition to said tire pressure.

7. The self-regulating tire pressure system of claim 4, said valve including a housing with an inner peripheral recess, said prestressed diaphragm being lodged in said re-cess to allow a restricted movement of said diaphragm with-in said recess when said diaphragm moves between bistable positions on opposite sides of its central plane, and fur-ther comprising an air impermeable flexible diaphragm span-ning said housing to block the flow of air therethrough, said flexible diaphragm being connected to move with said prestressed diaphragm.

8. The self-regulating tire pressure system of claim 2, said reference pressure source comprising a pressure regulator for providing said reference pressure from said high pressure reservoir at a predetermined regulated pres-sure.

9. The self-regulating tire pressure system of claim 1, further comprising means for sensing said valve's fre-quency of operation as an indication of a slow tire leak when said frequency exceeds a predetermined threshold.

10. The self-regulating tire pressure system of claim 1, further comprising means for sensing the number of valve operations and the duration of each such operation as an indication of a flat tire condition when the number of said operations for a predetermined duration exceeds a predeter-mined threshold.

11. The self-regulating tire pressure system of claim 1, further comprising means for sensing the duration of said valve's operation as an indication of a low reservoir air pressure condition when said duration exceeds a prede-termined threshold.

12. A self-regulating tire pressure system, compris-ing:
a wheel for seating a tire, said wheel including a reservoir for providing a high pressure air source, a valve for establishing an air flow communica-tion between said reservoir and a tire seated on said wheel in response to a low air pressure condition in the tire, and means for sensing the timing of operations of said valve as an indication of the type of low pressure condition.

13. The self-regulating tire pressure system of claim 12, said sensing means comprising means for sensing said valve's frequency of operation as an indication of a slow tire leak when said frequency exceeds a predetermined threshold.

14. The self-regulating tire pressure system of claim 12, said sensing means comprising means for sensing the number of valve operations and the duration of each such operation as an indication of a flat tire condition when the number of said operations for a predetermined duration exceeds a predetermined threshold.

15. The self-regulating tire pressure system of claim 12, said sensing means comprising means for sensing the duration of said valve's operation as an indication of a low reservoir air pressure condition when said duration exceeds a predetermined threshold.

16. The self-regulating tire pressure system of claim 12, said valve comprising a bistable valve having open and closed positions respectively establishing said air flow communication in response to a first predetermined differ-ential between said reference pressure and said tire pres-sure, and breaking said air flow communication in response to a second predetermined pressure differential between said reference pressure and said tire pressure which is less than said first predetermined pressure differential.

17. The self-regulating tire pressure system of claim 12, for a vehicle having said wheel mounted with respect to a vehicle chassis, said sensing means comprising a primary electrical winding on said chassis proximate to said wheel, means for delivering an alternating electrical signal to said primary winding to establish a primary winding flux field, a secondary winding on said wheel within said prima-ry winding flux field, a valve indicator means connected in circuit with said secondary winding for varying the second-ary winding impedance reflected back to said primary wind-ing according to whether said valve is establishing said air flow communication, and timing means responsive to said reflected a secondary winding impedance for timing operations of said valve.

18. The self-regulating tire pressure system of claim 17, wherein said means for delivering an alternating elec-trical signal to said primary winding delivers a pulsed signal with substantially constant current pulses, and said timing means is responsive to the voltage across said pri-mary winding.

19. The self-regulating tire pressure system of claim 18, wherein said means for delivering an alternating elec-trical signal to said primary winding delivers a pulsed signal with substantially constant voltage pulses, and said timing means is responsive to the current through said pri-mary winding.

20. The self-regulating tire pressure system of claim 17, wherein said secondary winding and valve indicator means comprise a tuned circuit with respect to the alter-nating electrical signal on said primary winding when said valve is establishing said air flow communication, and said timing means is responsive to a tuned resonance between said primary and secondary windings.

21. The self-regulating tire pressure system of claim 17, said means for delivering an alternating signal to said primary winding delivering a signal with a duty cycle sub-stantially less than 50%.

22. A method of regulating the air pressure within a tire seated on a wheel, comprising:
providing a high pressure source in said wheel, establishing a connection between said high pres-sure source and the tire in response to the air pressure within said tire falling below a predetermined low pressure threshold level, breaking said connection in response to the air pressure within said tire rising above a predetermined de-sired pressure threshold level which is greater than said low pressure threshold level, and sensing the timing of establishing and breaking said connection as an indication of the type of low pres-sure condition within the tire.

23. The method of claim 22, said sensing step com-prising sensing the frequency at which said connection is established as an indication of a slow tire leak when said frequency exceeds a predetermined threshold.

24. The method of claim 22, said sensing step com-prising sensing the number of times said connection is es-tablished and the duration of each such connection as an indication of a flat tire condition when the number of times said connection is established for a predetermined duration exceeds a predetermined threshold.

25. The method of claim 22, said high pressure source being provided from a high pressure reservoir within the wheel, said sensing step comprising sensing the duration of the connection each time said connection is established as an indication of a low reservoir air pressure condition when said duration exceeds a predetermined threshold.

26. A bistable valve that is actuated in response to a variable pressure falling below a first pressure set point and is deactuated in response to said variable pres-sure rising above a second pressure set point that is greater than said first set point, comprising:
an air flow passageway, a reference pressure source, and a bistable diaphragm for receiving said reference and variable pressures on opposite sides of the diaphragm, said diaphragm having first and second stable positions first opening and then closing said air flow passageway in response to said variable pressure first falling below said first pressure set point, and then increasing above said second pressure set point.

27. The bistable valve of claim 26, said bistable diaphragm comprising a prestressed diaphragm oriented about a central plane and having stable positions on opposite sides of said central plane.

28. The bistable valve of claim 27, said reference pressure source comprising a sealed bellows with an inter-nal pressure establishing said reference pressure, said sealed bellows bearing against said diaphragm in opposition to said variable pressure.

29. The bistable valve of claim 27, said reference pressure source comprising a mechanical spring bearing against said diaphragm in opposition to said variable pres-sure.

30. The bistable valve of claim 27, said reference pressure source comprising a pressure regulator for provid-ing said reference pressure from said high pressure reser-voir at a predetermined regulated pressure.

31. The bistable valve of claim 27, said valve in-cluding a housing with an inner peripheral recess, said prestressed diaphragm being lodged in said recess to allow a restricted movement of said diaphragm within said recess when said diaphragm moves between bistable positions on opposite sides of its central plane, and further comprising an air impermeable flexible diaphragm spanning said housing to block the flow of air therethrough, said flexible dia-phragm being connected to move with said prestressed dia-phragm.

32. The bistable valve of claim 26, said bistable diaphragm comprising a flexible membrane carrying a first magnetic member, said valve further comprising a second magnetic member aligned with said first magnetic member, at least one of said magnetic members being magnetized to hold said magnetic members together with said diaphragm in said second stable position when said variable pressure exceeds said second pressure set point, and to allow said diaphragm to flex away from said second magnetic member to its first stable position in response to said variable pressure fall-ing below said first pressure set point.