Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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Hydrostatic adjustin~ device, more particularly
a steering mech~nism for motor-Yehicles.
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Tht- inventicn rel~tes to a hy~rost~tic adjusting device, nnre parti-
cul~rlJ~ ~ ~teering rnech~nis~ for motor-vehicles, having an oper~tin~
circ~it com~ isin ~n adjusting motor, a control-vale connected thereto
b~ k2~s ~nd adjustable b~ means of a actuating element, and a leedbac~
~evice re,;ro~ucin~the position of the adjusting r.lotor b~ using a pressure-
mcdiu~ line, the said feedback device acting in a direction onposite tG
~:c~t oi tne seid actuztin~ element.
In one }.n.own adjustin~; device of this kind (German Pat~nt 12 93 029),
the f ecdback device comprises an inte~rating ~ ~ea~r~g) motor ~Ihich
is com~ined structurall~r ~;tith the control-valve and is driven by the
pressure-mediu~ Ilowin~ to the said adjusting motor. Since t:.e adju~tin~
r~o~el:~ent of the integrating motor is proportional to the adjusting
movernent of the adjusting motor, this provides the desired feedbac~-
ef~ect, ~Jith no need for a mech~nical conrlection between the a~justing
motor nn~ the control-valve- This has the advantaGe that t'ne adjusting
l.lOtO need be conllected to the control-valve only by the prcssurc-me~ m
lir.cs, ~;.;ich provi~es a ~xeat ~eal of freedom in arranging individual
prt~ .iti-l ~djustin~ devQces oI this ~;ind, ho~7ever~ there eY~ists, un~er
cer~in circu~st~r.ces (hi~h operatin~ pres~urcs, heavy ~Jear, ~tc. )
dan~cr of drift, i e the adju5t~nent of the integxating motor is not
exactly proporti~.nal.
hlso kno~n (Ger~an ~S 26 29 113) are adjusting devices comprisin~ ~
purel~ mechanical feedbacl . Although these are drift-free, the control-
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v~lve must be connected mechanically, not only with the actuating device,but also ~ith the adjusting motor. Thi8 results in considerable impair-
ment of the overall design and assembly.
It is the purpose of th~ invention to provide a hydrostatic adjusting
device o~ the type mentioned at the beginning hereo~, i.e. having a feed-
back eIfected only by a pressure-medium line, such that leaks in tne
system do not produce drift.
~ ccordin~ to the invention, this purpose is achieved in that the
actuating element acts upon t~,e control-valve through a srring, and the
adjusting motor acts upon ~the-pressure-relief valve through a spring,
and in that the feedbac~ device comprises a hydrostatic ~eedbacl; circuit,
the pressure in which is determined by the said pressure-relief valve
and acts upon a pressure-surface on the said control-valve
I~ this ~sign, the E~osition of the adjusting motor is converted,
Wit~! tl-!e eid of a spring and a ~ressure-relief valve.into hydrostatic
pres~ure. The control-valve assumes a position oi e~uilibriu~ whic.. is
a function, on the one hand, of this hydrosthtic feedback pressure an~,
on the other hand, of a s,3ring, the force of vJhich is determined by the
position of the actuating element. Ieakage losses in the operati~g
circuit play no part in this , since it is merely a matter of the position
of the adjusting motor. Ieakare losses in the feedback circuit are also
immaterial, sir,ce the feedback pressure determined by the pres~ure-
relief valve i~ not in~luenced ti.erehy.
The advanta~es of a drift-free feedbac~ and flexible assembly are thus
comblned.
The operating and feedback circuits may be completely separated from
each other, each being sup~lied from its o~n source of pressure-medium.
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Ho~ever, the feedback circuit and pressure-relief valve may be fitted
between the inlet-e~d ol the control-valve and the tank. This makes it
possible to manage with a single source of pressure-medium or pump. A
particl~larly lo~-power design is obtained by locating the ~eedback
circuit an~ pressure-relie~ vaive between the outlet-end of the control-
valve and the tank, s~nce in this way the pressure-fluid is use~ twice.
In one preferred exPmple of embodiment, the pressure-valve comprises,
between inlet and outlet, t~o series-circuits of t~o chokes each, from
the junction-l~oints of vihich, tr-e operating lines branch off, the chokes
~ithin each series-circuit, and the similar chokes of each series_circuit,
~eing adjustable in opposite directions. In this way, the position of
the adjusting motor is given by a pressure-equilibrium. ~.ach adjustment
oI the control-valves leads directly, i.e- ~ithout any lost motion, to
an advusts~ent of tht adjusting motor. In addition to this this, pressu.e-
llui~, at ~rl adeo,uate pressure-level, is always av~ilable at the out!ut
fro~ the control-valve, in order to supply the feedback circuit.
~ particu.arly sim~le desi~n is obtained if the control-val.e comprises
a piston, one end-face of which i~ loaded by the relev~ spring while
the ot~er conEtitutes the pressure-surface exposed to the pressure in
the leedback circuit.
It is also advantageous if- the spring on the ~ide fa~ing the adjust-
ing motor and the actuating element rests upon a supporting piston de-
fining a compensatin~-pre9sure chamber conlected to the ieedback circuit.
Thi~ prevents the feedback pressure ~rom having any effect Y~hatever upon
the po~ition of the adjusting motor or of the actu&ting element.
In another confuguration of the invention, the act-uating element may
be connected to a hand-pump, each connection to which is connected, via
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a non-returli valve open towards the source o~ pressure-me-dium~ to the
pressure-side thereof and to the feed-5ide Gf the contr~l-valve. This
~n~-~ump ensures that the actuating elment may be adjusted, in normal
operation, c-lmo5t without force, since the pressure-fluid supplied from
thc pressur-medium source flows thrDugh the said han~-pump. However,
there i9 an autOmatic~imit to the.speed of adjustment, if the
pre~sure-medium source can no longer sup~ly sufIicient pressure-~luid;
in which case adequate force must be applied to the actuating element.
The hand-~pump may al80 be used as an emergency_pump.
~ ccording to one particularly favourable desi~n, the hand-pump delivers
per nnit of travel at leasl the same amount of pressure-fluid as the
adjusting motor per unit of travel. This allov~s emergency operation, in
which even the feed-back circuit remains operatiYe.
It is also desirable for the pressure-side of the pressure-medium
source to be conriected to the tank through a suction-non-return valve.
In thiC wa~, in the event o~ failure of the pressure-medium source,
the s~id oUrCe is bridged by the said suction-non-return ~alve.
The invention i9 explained hereinaftc~ in greater detail in con-
junction Y~ith the proferred example of embodiment illu~trated in th~-
drawing attached hereto, in which the sole fi~ure is a circuit-dia~ram
of an adjusting device according to the in7ention.
An operating circuit O comprises a pressure-medium so~rce 1 in t~e ~orm
of a pum~, a control-valve 2 and and adjusting motor 3. The pump draws
prc-ssure-Iluid irom a tank 4 ahd delivers it, from pre6sure-side 5,
through two pairs of non-return valves 6,7 and 8,9, to inlet-si~e 10
of control-valve 2. The adjusting motor comprises a pislon 12 moving
in a cylinder 11, pigton_rod 13 acting upon the mechanism to be adjusted,
e.g. the wheels to be steered- The 8aid pi8to~ separates two operatlng
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cha~bers 14,15 from each other which are connected, thro~gh motor-leads
16,17, to motor connections 18,19 on control-valve 2.
Outlet-side 20 of the control-valve is no`t connected dircctly Y~it~.
i'and a tank-line 2
tank 4, but through a feedback circuit 21, 2 pressure-relief~~~ 7
~eedback circuit 21 comprises a pre89ure-medium line 24 which connects
to,ether a pressure-chamber 25 and a p~essure-chamber 26. ~ressure-
relief valve 2? has a slide ~7 loaded on one side by a spring 28 ~hich
bears upon a supporting piston 29 secured to piston-rod 13. ~eft-hand
end-face 30 forms, in conjunction with a val~e-seat 31 inter-ral ~ith
the housing, the cho~e-point o~ pressure-relief-valve 22. Slide 27
assumes a position of equilibrium which i8 dependent, on the one hcn~,
upon the pôsition of adjusting motor 3 and the compression of sprinr
28 produced thereby and, on the other hand, upon force P1J which is e~ual
to the siz.e of end-face 3L times pressure ~ in ~eed-back circuit 21.
Since pre~sure ~ is set by ~ressure-relief valve 22, this pressure is
an accur~t~ insication o~ the position of adjusting motor 3. r
Control-velve ~ comprises a pi~ton 32, one end of ~hich is 'oade~ by
a sprir.g 33 be&rin6 upon a supporting piston 34 adapted to be displaced
axisll~ by an actua~ting element 35. ~cting upon the other end ol piston
32 i~ ~ force P2 which is equal to the size of end-face 36 times pressure
. As a result of this, the position of adjusting motor 3 is fed ba~k a~
pressure ~ to controi-valve 2.
Located behind supporting piston 29 i8 a compensationg chamber 37,
and located behind compensating pi8ton 34 is a compensating chamber 38.
~oth chambers are connected by a compe~-~sating line 39 to the restorin~
circuit, in order to prevent any reactive effect of restoring pressure
upon the position of the adju~ti~g motor or of the actuating element.
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~ otor-cor.nections l~ls on con;rol-valv- 2 run from annular grooves
39,40. The piston comprises t~o lands (? shculders, collars) 41,42 which
Pepar~te two inlet-side annular grooves 43,44 ~rom an outlet-side annular
Frocve 4~ on the piston. This produces tVJo series-connected chokes A,3
an~ C,D, chokes A and ~ varying-jointly in one direction, and chokes
an~ C varying 30intly in th~ other direction, as the piston is dis-
placed.
~ ctuating element 35 is connected to a hand-pumo 46 co~prising a
cylinder 47, a piston 48 and a piston-rod 49. One pressure chamber 50
is c~nnected to a point 51 between non-return valves 6,7, while the
other pressuIe chamber 52 iS conr~ected to a point 53 betY~een non-return
vzlves 8,9. ~oreover, pressure-side 5 of pressure-mediurn source 1 is
conntcted, through a non-return valve 54, to tank 4.
The method OI operation of this arrangement is as follows.
~ ihen, durin~ normal operation, adJusting motor 3 is displace~ by a
~istance ~1, Spl ing 2~ is compressed accordingly. This produces a
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position of eqvilibriu~,. of slide 27, in ~hich-:
Pl z Cl . xl,
wherein Cl is the spring-constant of spring 28. Since pressure-relief
v~lve 22 adjusts itself to this position of equilibrium, a feedback-
pressure P, proportional to force Pl, is established in feedbac~ circuit
21. If the displacement of the actuating element is designate~ x2, this
als~ produces a poaition of equilibrium of ~iston 32 in control-valve 2
in accordance with:
P2 = C2 . x2,
wherein C2 is the spring-constant of spring 30.
If piston-rod 49is mo~ed to the left by actuating ele'ent 35, the
pressure in motor-connection 19 rises while that in motor-connection 1&
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falls.This causefi the piston in servo-motor 3 to move to the left, com-
pressin~ spring 28 and increasing feedback pressure ~. This restores
~iston 3~ of control-valve 2, against the force of spring 33, to the
central position. The same a~plies if actuating element 35 is moved to
the right. The chan~es in travel are ~overned by tile speed-ratio of the
apparatus. Inciuded in this speed-ratio are the spring-constants of
prings 28 and 33 and the areas of end-faces 30 and 36. In this connection,
any leakage losses in feedback-circuit 21 are without significance.
If it is noY~ assumed that a disturbing force S acts, from t-~le outside,
upon adjusting motor 3, piston-rod 13 will be shifted slightly to the
left. 1.8 a result of this, feedbac~lpressure ~ rises and moves piston
32 sli~htly to the right. The resu~t of this is that the pressure in
operating chamber 14 rises, until disturbing fGrce S is compensate~ fo~,
If this produces leakage along piston 12, thi~ is immaterial, since
pressure-medium source 1 sup~lies an appropriate amount of fluid and
feedback-pressure ~ is not affected. If actuating element 35 i8 ad-
juEted and a disturning force S acts Eimultansously , the two previously
~ecribe~ ~unctions are superimpo~ed over each other in the correct
~irection.
Wher servo-mQtGr 3 is adjusted, the pressure-medium sup~,lied divides
into one part which pa8ses directly through the chokes to outle~ æide
20 and another part which passes through the said motor to the outlet-
side. In any case, sufficient pressure-medium to produce feedbacX-
pressure ~ is available in feedback circuit 21. ~ ;
The move~ient of actuating element 35 is suFported by hand-pump 46
since, ~hen piston 48 is displ6ced, pressure-medium source 1, supplies
fluid to the suction-6ide, whereas the pres6ure-fluid from the pressure-
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side of the hand-pump passes to pressure-side 10 of control-valve 2.
Hand~pump 46 is loaded only when actuating element 35 i9 moved so
fast th&t the amount of pres~ure-fluid available from pressure-medium
ource 1 is no longer sufficient, and increased resistance will be felt
~t the ~aid actuating element. Irhis provides the driver of a vehicle,
for example, viith important information that the syste~ is being ad-
justed too quickly since, in the case of a di9placement to the right,
for example, if the hand-pump delivers a larger amount of pressure-fluid
than pressure-medium source 1, the pressure at point 5 and in operating
chamber 50 dro~s, whereas the pressure in operating chamber ~2 is held
to to a level predetermined by the external loadin~ of the system. ~or
this reason, non-re~urn valves 7,~ are closed at this time. If the
pressure at point 5 drops below tank-pressure, pressure-fluid will be
dra~n through non-return valve 54.
A special case in the la9t-considered operation is emergency-contr
i.e. when pressure-mediu~ source 1 fail9 to deliver any pre~sure--~luid.
In this case, hand~pump 46 providea all of the pov~er. Pressure-fluid
is dra-,n t~rou~h non-return valve 54 and i9 released through non-return
valve~ 7, 5. If the ~eedback-cirouit i8 to operate correctly un~er
theEe conditions, the hand-pumo must dis~lace an amount of fluid at
lea~t as ~reat as that displa ed by piston 12 in ad3usting motor 3. In
this way, feedback-control is maintained, at lea~t approximately, even
during emer~ency operation.
In the dra~Jing, the adjustin~ deYice according to the invention is
described in connection with movements of translation, but designs may
also be used in wLich movement~ or rotation, or combinations of rotetion
and translation, ariRe. ~or example, the adju~ting motor muy act upon
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the track-rod of a steering mechanism, while the pressure-
relief valve is fitted to the relevant kingpin, so that the
adjustment is carried out in rotation.
It is also possible to arrange feedback circuit 21
in parallel with operating circuit 1, i.e. to branch it off from
pressure side 10 of control valve 2. Moreover, feedback circuit
21 may also be provided with its own pump.
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