CA1113016A - Steering valve - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE

A hydraulically operated steering system for vehicles has an actuating means and an adjusting motor for the steered vehicle parts. The actuating means is constituted by a rack of a rack and pinion steering gear. The adjusting motor has two working chambers with which are respectively associated pairs of spring-loaded seated valves. Inlet valves are provided which are connected to a hydraulic pressure accumulator, via hy-draulic lines and to the respective working chambers of the adjusting motor via further lines. Each inlet valve comprises a valve seat, a valve member constituted by a ball and a compression spring which is located in a spring chamber of each inlet valve and which urges the ball against its seat. The two inlet valves are connected via springs in opposite directions to the actuating means. Outlet valves are connected to the respective working chambers of the adjusting motor via hydraulic lines and via a common return flow connec-tion to a reservoir. Each outlet valve comprises a valve seat, a valve member and a tension spring which urges the valve member against its seat. The outlet valves are connected via springs to the actuating means. A piston rod and piston of the adjusting motor are arranged fixed on the vehicle, while the cylinder casing thereof is movable in relation to them. The valve seats are rigidly connected to the cylinder casing of the adjusting motor. In the neutral position of the steering system in which the actuating means is free from force the inlet valves are closed. They are adjusted to a pressure which is somewhat higher than the pressure in the accumulator. Both outlet valves are open. Both working chambers of the adjusting motor are un-pressurised.

Description

L13~

This invention relate~ to a hydraulically operated 3teering sy~tem, particularly for vehicle~, having a ~teering ~alve arrangement, wherein the supply from a pre~sure source i9 closed in the neutral position of the valve arrangement. In contrast to a steering valve arrangemen~ requiring a continuou~ neutral flow of the hydraulic medium, a ~teering ualve arrangement of the foregoing kind affords the advantage that les~ energy i~ consumed when the steering ~ystem i8 not operated, ~ since there are no circulation 14~ses~
; Steering valve ar~anyements of the ~oregoin~ Xind are malnly for use i~ hydraulic steexing systems - i.e., steering systems in which there i8 a mecha~ical connection ~etween the actuating means (steeri~g whsel) and an adjustin~ motor for the vehicle parts to be ~teere~.
Hydraulic boosting i9 re~uired only when the vehicle travel~ along cu~es, but not whe~ it i~ ~ravelLin~
~traight ah~ad, for exam~le on motorways, ~o that a ¢on-~iderable amount of en~rgy can be ~aved when driving strai~ht ahead.
The invention can also be applied to hydrostatic ~teering sy~tems - i.e., steering sy~tems in which there i~ no rnechani~al conrlec~ion between the actuating ~eans and the a-~justing motor. It i8 true that vehicle~
equipped in thi~ way are not permitted to reach high ~peeds. ~everthele~s, in this ca~e also energy 108~
due to the circula~ion of the hydraulic medium i~ to be ~3~

avoided if a particular ~teering movement remains un-changed, for example, w~en a working vehicle performs work with a qteering movement un~h~nged, at re~t ~r in movement.
Steering valve arran~ements are al80 kncwn from German Of~enlegungs~hriften ~03. 21 31 276 and 24 46 841 ( ZF, Jablonsky ) O In the prior art steering valve arrange~
ment the inlet valves, which form components of the ~teer-iny val~es, are constructed as seate~ valves which are cloJed in the neutral position. No circulation los~es therefore oc~ur. If the actuating means is operated beyond the response clearance, one ~eated valve is~opened, and a workin~ pressure build~ up in one working chamber ,~
of the adjusting motor, namely that particular presqure chamber. A particular design o~f the inlet seatJd valves ensure~ that a reactio~ force p~oportional to the work-in~ pressure i5 e~erted on the ~eJted valve~, such reaction for~e being perceptible at the actuating means (Jteeri~g wheel) and giving the driver the nec~essary road feel". : ~ ~
With a steering movement, a~ter the re~po~se clear-:
ance has been ~used up, the or each o~ the inlet se~ate~
ValVe8 i 9 opened by m~chanical abutment - i.e., when a connection between the a¢tuating means and the valve sucldenly becomes rigid. A~ a resul a~ axces3ive amount of pres3ure fluid sud~enly hoots in~o the particular pressure chamber of an adjusting motor required for the 3~

-4- ~

3teered vehicle parts. The consequence i5 un~teadiness ~;
in the ~teering operation, which has hitherto proved impo~sible to elimina~e in the known ~teering valve arrangements. '' A steering valve arrangement of a different kind with lnlet seated valve~ is also known from German Auslegeschr~ft No. 12 14 554 (Bosch)~ mi8 steering valve arrangement operate~ on the pre sùre-reducing principle a~d calls ~or an expensive construction.
The pre~ent i~vention aims at providing a ~eering valve arrangement whi¢h has inlet seated Yalves a~d is so constructed that no un~teadiness ~acurs during a ~teeri~g operation, althouqh the advantage of a pro-portional reaction from the pr~s~lure chamber on the actuatin~ mean3 i3 maintained. -~
Accordin~ly, the pre~ent invention cons.~sts in a hydraulically operated ~te~ering system, particularly~
for vehicles, comprising an actuating means and an adjusting motor, having two workinq chamber~, f~r the steered vehicle parts, worXing fluid ~upply llne~ which:
extend from a pre3sure source respectively to the work-ing cha~ rs o~ the ad ju~ting motor and contain ~wo inlet seated valve-q ~losed in the neutral po~ition of the steer-ing sy~tem, and return flow line~ which ex;te~d respectively from the ~orking cham~ers of said motor to a resenroir and contain two outlet valve3, the two inle~ seated valves being connected via ~ontrol springs i~ oppo~ite directions to the actuating means .

353~;

rrhe invention use~ a different principle from the prior art, namely a pure force control system to control the inlet seated valves~ ~hi~ is achieved by disposing the inlet ~eated valve actuating spring~, which are required in any case, in the line of the linkage. The seated valve ~tarts to open when a given force (so-called limit force) has been reached. However, after the limit ~or~e has been overcome, the pre~ure in th~ pres~ure chamber of the adjusting motor can build up only steadily, so that no un~teadine3s ~a~ occur in the steering operation.
In the adjoining propQrtionality zsne (i.e., in the zone of steerin~ movements, in which reaction ~orce proport- -ional to the working pres ure can be felt at the actuating means~, the springs ~f tha inlet seated valves have the effect of control sprin~s for the inlet seated valves operating a3 pre~sure-limuting valve~.
It is immaterial to the principle of the in~ention whether the force transmitte~ to the control spri~gs i~
picked up directly from a ~teering ~pindle, a part of a ~teering transmis~ion, or a part ~ownstream of the steer-ing transmission.
It is true that in the neutral position of the:
~teering ~y~tem the steering valve arra~gement3 known from the two above-mentioned German Offenlegung~schriften prevent any flow of hydraulic medium. In cont~a~t, however, hydraulic medium mu~t flow con~t~ntly i~ ~he driver when driving straight ahead mu~t constantly perform counter steering to some extent on a road which falls away ~o one ~ide, or with a side wind~ Then neceqsarily one of the inlet ~eated valves is opened, and flow losse~ oc~ur ayain.
According to a~ optional feature of the invention the two outlet valves are also constructed as seated valve3 a~d axe actuated by the actuati~g me~n~ via their control spxings. ~hi~ha~ the adva~tage that even when the limit force is overcome and pres~ure medium flow~ vi.a one inlet ~alve to the adjustin~ motor, a~y leaka~e flow to the!reservoir i~ pre~ente~. If the steering wheel i8 merely held ~a t by force, but not rotated, no pre~ure medium i8 re~uired either. This applies to driving with a side wind ~r on a road sloping to one side.
~ further advantage of the~foregoin~ optional feature is that at lea~t each pair of valves ~inlet and outlet valve associated with one working chamber) can be actuated by t`he same constructional member of the actuat-ing mean~, ~o long as ths outlet valve always holds the balance to a pres~ure greater by a differential p~res~ure than the associated inlet valve.
It i3 therefore ~imple to aetuate the valves. ~his advantage i~ achieved by the ~act that pure force control iS al90 u3ed ~or actuatin~ the outlet valve~qO
In the simplest ease the spring chamber of the iniet and outlet seated valves are connec~ed to the as~oc-iated working chamber of the adjusting motor. Consequently L3~

the force control of these valve~ also must come into effect in a cham~er at working pressure. According to a ~urther optional feature of the invention this can be avoided by using pre~sure-balanced inlet seated valve~.
ThQ power steering for these valves can then bs accommo~
dated in a pre~sure-relieved chamber.
If t~e inlet and outlet ~eated valves are equipped with separate control springs, it can be difficult to maXe sure that both valves hold the bala~ce over the whoIe pro~ortionality range to pressures which differ by a predetermined dif~erential pressure. This difficulty can be overcome by a further optional feature of the inventlon, namely the use of a balance beam for each pair or both pairs of valves. In that ca~e a common control spring acts on the inlet and out;Let valves, while an additional spring ensures~that the differential pressure i~ maintainad over the proportionality range. There i~
th~refore no need to adapt to one another within ~lose tolerance3 the rigidities of two ~pring~ and the seat cross-3ection of two valve~ of each pair.
Beyond a predeterm~ned value of ~teeri~ mo~ement~, ~uch as i~ exceeded when parXiny, a ~roportional reaction on the actuating system is DO lo~ger nece~ary, although i~ i8 desirable for the maximum working pre3sure to b~
available in the particular pressure chamber o~ th~
adjusting motor~ The so-catled cutti~g-off effect must occur - i.e., the proportionality ~traight line must be cut off. ~ftex the cutting-off point has been reached, the working pressure should reach its maximum value without any appreciable increase in the force exerted on the actuating system. To this end a very e~pensive con-struction is required for the aforementioned ZF steering valves, since two additional steering limiting valves must be provided. In the case of the aforementioned German Auslegeschrift 12 1~ 554 the cutting-off effect cannot be achieved at all~
By a further optional feature of the invention the cutting off effect, with the use of a ~alance beam, can be achieved in very simple manner, namely by stops which limit the zone of operation of the control springs.
In one aspect of the present invention there is provided a hydraulically operated steering system particularly for vehicles, comprising an actuating means and an adjust-ing motor, having two working chambers, for the steered vehicle parts, working fluid supply lines which extend from a pressure source respectively to the working chambers of the adjusting motor and contain two inlet seated valves closed in the neutral position of the steering system, and return flow lines which extend respectively from the work-ing chambers of said motor to a reservoir and contain two outlet valves, the two inlet seated valves being operatively connected via control springs to the actuating means for transmitting a valve operating force in opposite directional senses to the respective inlet valve in response to dis~
placement of the actuating means from the neutral position, whereby a regulated pressure proportional to the valve operating force is established in one of the operating cham-bers to which pressurised ~luid is conducted by one of the inlet valves.

~3~
In a ~urther aspect of the present invention there is provided a steering valve arrangement for use in a hydraulically operated steering system, comprising supply lines which extend from a pressure source respectively to the working chambers of an adjusting motor and contain ~-two inlet seated valves closed in the neutral position of :
the steering system, and return flow lines which extend respectively from the working chambers of said motor to a reservoir and contain two outlet valves~ the two inlet seated valves ~eing operatively connected via control springs to an actuating means of the steering system for transmitting a valve operating force in opposite directional senses to the respective inlet valve in response to displacement of the actuating means from the neutral position, whereby a regulated pressure pro~
portional to the valve operating force is established in one of the operating chambers to which pressurised fluid is conducted by one of the inlet valves.
In order that the invention may be more readily understood, reference is made to the accompanying drawings which illustrate diagrammatically and by way of example embodiments thereof, and in which:-Figure 1 illustrates the principle of the force control system, Figure 2 shows a part of a steering system having two pairs o~ inlet and outlet seated valve which are jointly controlled, Figure 3 shows the various steering zones, repre-sented by graphs, Figure 4 is a longitudinal section through an embodiment of the invention having a balance beam by means of which a pair of seated valves is controlled, , -8a-Fig.5 ~hows a ~imilar embodiment of the invention, incorporated in a rack and pinion steering sy~tem, E~igs.6 and 6a are a longitudinal section and a cro~s-section along line a-a in Fig.6 re~pectively, of a further embodiment of the invention, in which a co~mon balance beam control~ two pair~ of inlet and outlet valve~ on the primary side of a steer-ing transmi3~ion, Fig.7 shows part of a rack and pinion steering sy~tem in which valv~ control~ according to another embodiment of the invention having resilient strip-like balance beams are provided on the ~econdary side of the steering transmlssion, and Fig.8 shows a further embodiment of the invention, applied to a hydro~tatic steering system. ~.
Steering valve arrangement with seated valves and control spring~:
Fig.l show~ an inlet ~eated valve 2 disposed in a supply line 3 extending from a pressure accumulator 4 to one working chamber of an ad justing ~otor (not shown).
The inlet seated valve 2 has a valve ball 6 and a valve seat 8. The clo~ure or control spring 10 i~ disposed bet~en the valve ball 6 and a member 12 whi~h is mechanic-ally driva~ly connected to an actuating means, that i~ a steering wheel (not sh~wn). A~ a rule the actuating means has a ~eparate centring devi~e, illustrated diagrammatic- .
ally in Fi~l by spring~ 14. However, the function of the ~

centrin~ device can also be performed by two control spring~ arranged in opposite directions. The same valve arrangement must al50 be imagined on the opposite side of the member l2. The spring chamker of each of these inlet seated valves is connected to one of the working chamber~
of the adjusting motor. The valve performs the function of a pressure-limiting valve. In depandence on its actu-ation, the mem~er 12 adju~ts the suitable working pre~sure in the pressure chamber of the adjusting motor~ ~he centriny springs 14, which are con~tructed as helical compression spring~ in this embodiment, are more conven-iently constructed in known mannex as a bending rod, torsion rod or cup ~prings.
Function.
The control ~prin~ 10, centring springs 14 and valve cross-section are ~o adapted to one another that in the neutral position, when the actuating means i~ free from ~orces, they hold the balance to a presaure which i3 slightly greater than the accumulator pressure in the supply connection 3. As a result in the neutral position the supply connection i~ reliably closed. If the member 12 is adjusted ~o the right (as viewed in Fig.l), the force acting from the right on the valve ball 6 decrea~es due to the expanaion of the control ~pr.ing 10, until finally the presaure in the ~upply connection 3 overcome~
~he force of the spring 10 and lift~ the valve ball 6 off its ~eat. Pres~ure fluid can then flow from the pressure --ll--accumulator 4 into the pressure chamber of the adju~ting motor. The ~ifferential pressure between the pres~ure accumulator and the adjusting motor pre~sure chamber i~
held by the control spring 10. After the actuating means has exceeded the limit force, there is proportion-ality betw~en the actuating force F and the working pressure p in the respective pre~sure chamber of the adju~ting motor. Fig.3 show~ these relation~hips. With a ~teering movement of 0, the pres~ure ~ in the adjusting motor fir~ remain3 0, until the limit force G is reached.
Then the pressure ~ rise~ proportionally to the force F
exerted at the ~teering wheel along the straight line 16.
In vehicle steering sy~tems the limut force i9 very desirable, since hydraulic boosting i8 preferably avoided in the range of small steering movements and steering forces, to improve road contact.
When the limit force is exceeded, a soft transition is obtained, ~ince as a result o~E the arrangement o the control spring between the actuating mean~ and the valve member, the latter opens gradually in correspondence with the increase in act~ating force.
The absen~e of any rigid connection between the actuating means and the valve member has the further advantage that a seated valve can also be used a the outlet valve, and this i~ impo~ible for manufacturing rea~ons with a rîgid connec~ion (Fig~4).
Steeriny valve arran~ement having four ~eated valve~.

` -~12-Fig.2 diagrammatically illu3trates a steering system with pure seated valve control. A~sociated with each of the worXing chambers 20, 20' of the adjusting motor 21 i~ a pair of valves, for example, one inlet ~eated valve 22 and one outlet seated valve 24 being associated with the working chamber 20. The same applies correspondingly to the working chamber 20'. The con-structural members in the right-hand half of the drawing have the same references with an index. To the extent that the arrangement i8 symmetrical, details will be described only a~ regards the left-hand half of the drawing. They apply ~imilarly to the right-hand half.
~rhe inlet seated valve 22 has as the control spring 26 a compres~ion spring which force~3 its valve member 28 again~t the valve seat 30. The outlet seated valve 24 has a control spring 32 conqtructed a~ a tension spring which pulls the valve member 34 against it~ seat 36 when appropriately actuated. The outer end~ of the spring~
26, 32 are attached to a rigid, tongs-like shaped member 38 of the actuating means. The member 38 has a rack 40 which can be adjuQted in the direction indicated by the double arrow 44 by a pinion 42 which can ~e rotated from the steering wheel (not shown~.
~ he pi~ton rod 46 and piston 48 of the adjusting motor 21 ar~ arranged fixed on the vehicle, while the cylinder casin~ 50 can move in relation to them. The valve seat~ 30, 36 are rigidly connected ~o the cylinder casing of the ad~usting motor. The spring chambers of the control springs 26, 32 open into the working chamber 20, thi~ being illuqtrated diagrammatically i~ Fig.2 by lines 52, 53~
~ The 9upply connections 3,3' of the inlet ~eated valve~ are connected ~o the pre3sure accumulator 4. A
common return connection 58 of the two outlet seated valve~ i3 connected to a reservoir 59.
In this embodiment no ~eparate centring device is u3ed, ~ince with 3uitable dimen~ions the control ~prings 26, 32 etc. can also perform this function.
Operation:-In the neutral poQition (Fig.2) in which the actu- -ating member 38 i8 free from forces, the inlet valve~

2~, 22' are closed. They are ad~usted to a pressure which i9 somewhat higher than thel preqsure in the pressure accumulator 4. Both outlet valves 24, 24' are op~ned.
Both pressure chamhers 20, 20' of the adju~ting motor are unpressuri~ed.
When the ~teering wheel i~ rotated and the pinion 42 moves the actuating member 38 to the right ~a~ viewed in Fig.2~, the control spring~ set to ~uch movement a resistance which can be ~elt at the ~teering wheel. W~en a~ter a predetermined displacement the limut force G
~Fig.3~ has been rea¢hed, the control spring 26' i~
expanded to such an extent that the pre~sure in the pre~sure accumulator 4 overcome~ the spring force and the :~Lh~3~L6 pressure fluid can flow into the working chamber 20', which then becomes the pressure chamber. sefore this condition i9 reached the outlet seated valve 24' has clo~ed, and its control spring 32' has been tensioned.
The inlet and outlet valves are so adapted to one another that the outlet valves always hol~ the balance to a pressur~ which is greater by a differential pre~sure ~p than the pressure to which simultaneously the inlet valves hold the balance. Con~equently at no operating position of the steering system can pre~sure medium, which i8 to be fed to the adjusting motor pressure chamber, flow away fxom the outlet valve connected thereto.
With the movement of the ,actuating member 38 to the right, the control spring 32 of the outlet seated valve 24, which is connected to the pre~sure-relieved working chamb~r 20, remain~ exp,anded, so that the work-ing fluid can flow away to the reservoir 5~. During this whole operation the inlet seated valve 22 ha3 remained closed, While a pressure equ~l to the accumulator preq~ure minus the pressure gradient at the inlet valve 22' build~
up in the pres~ure chamber 20', the cylinder casing S0 of the adju~tin~ motor move~, The rigid connection of the valve seat~ to the casing produce~ a control circuit ~hich makes the cylinder to follow up the movement of the actuating member 38, In Fig,3 the straight line 16 shows the relation-~hips at the respective inlet seated valve in operation,namely the pre~sure ~ regulated thereby in dependence on the actuating force F exerted on the ~teering wheel. As already ~tated, in each case the associated outle~ seated valve holds the balance to a pre~ure highex by pre~ure differential ~p. For the outlet valve the str2iyht line 60 i~ obtained which, as illustrated in Fig.3, ideally extend~ parallel with the straight line 16. In no ca-~e may the twa straight lines intersect one another. This would mean that the inlet and outlet valve of the ~ame ~ide are open qimultaneou~ly - i.e., that pres~ure medium could flow directly from the accumulator to the reservoir, by-pa~ing the adju~ting motor. If in con-trast both 3traight line~ always have a distance ~p, namely a safety hysteresis freel~y 3electable in principle, the pr~s~ure fluid must always follow a cour~e via the adju-~ting motor. The ~traight line 60 in~ersects the F axi~ at a point S. The distance O - S repreqent~ the increase in actllating force within the clearance of the ~pring 24' of the outlet valve.
If the qteerin~ ~ystem i~ not actuated from the -qteerin~ whe~l, but from the steered wheels, for example when returning from taking a curve to driving ~traight ahead, and the actuating means is in or adjacent it~
neutral position (between 0 and S in Fig.3~, both outlet valves 24, 24' are opened, and there is an unimpeded working f luid ci rcuit between the working chambers o th~

, . ' ~ .

f~

adjusting motor and the reservoir. The cylinder casing 50 and the steered vehicle wheels can therefore move unimpeded in both directionq.
If after a steering movement at a curve the driver doe~ not completely relea~e the steering wheel but merely allows it to return 910wly with braking, the actuating member 38 again being moved from the end position whi~h it has reached, for ex~mple on the right, to the left, first of all again the force of the control spring 26 ' of the inlet valve increases, and the supply from the pressure accumulator 4 is cut off. When the actuating force ha~ been reduced by a value ~F corresponding to the differential pre~sure Ap, the outlet valve 24' opens, and pressure fluid can flow away to the re~ervoir.
Thereafter the control spring 32~ expandsd, and as more pressure fluid flows away from the pressure chamber 20', the pressure at the outlet valve drop~. The ~traight line 60 (Fig.3) i8 passed through in the direction indicated by the arrow - i.e., downwards - until finally the point S is reached and the working chambers are pre~sure-relieved. During the return steering operation, therefore, al~o the pressure in the pres~ure chamber of the adjusting motor ia clearly associated with a force at ths steering wheel.
Cuttin~-off effect.
Beyond a prede~ermuned actuating force at ths steering wheel there is no advantage in a further L3~

proportional increase in force. ~ore particularly during parki~g it is undesirable that the steering force ~hould increa~e appreciably. However, at the same time there is no advantage in any feedback of the forces acting on the vehicle w~eel~. The proportionality range, repre~ented by the straight line 16 in Fig.3, ~hould be cut off beyond an actuating force A. Then the pre~ure in the preQSure ch~mber increases steeply along the straight line 62 without any appreciable increase in actuatin~ force. ~The portion 16a of the straight line has been cut off).
In a steering valve according to the invention the cutting-off effect can very si~ply be produced by the fact that the effect of the control springs iQ
cancelled out from a predetermined actuating distance and there~ore a predeterm~ned actuating ~orce onward~.
This i~ shown by all the following embodiments.
Pairs of valves with balance beam.
In the emkodiment~ illustrated in Figs.4 and 5 conQtructional member~ already described ha~e the same two-place references, but with a preceding 4 or 5, resulting in reference numerals in the hundreds.
Fig.4 shows the cylinder ca~ing 450 of the adjust-ing motor, its pi~ton 448 with a pi~ton seal 477 and piston rod 479. Only the left-hand half (as viewed in the Figure) of the pi~ton i9 shown, and therefor~ only one pair of seated valve~, namely inlet seated valve 422 and outlet seated valve 424. The ~ame valve arrangement must also be imagined in the right-hand pi~ton half. All four valves are therefore integrated in the piston. To avoid difficulties when adapting the valve springs to one another, in this case an inlet valve and an outlet valve are each jointly actuated by a balance ~eam 464.
The inlet valve 422 has no control spring of its own, but both valves are actuated via a common control spring 466 arranged in the centre of the balance beam. The control spring enclo-~es a stop pin 468. The actuating means acts on a tappet 470 which is centred by means of cup springs 472.
The control spring 466 acts via balance beam 464 with e~ual forces on inlet valve 422 as it doe~ on the outlet valve 424. To keep the outlet valve 424 free from forces in the neutral po~ition, when the inlet valve 422 is closed, an additional spring 474 i5 re~uired whose prestressing i9 approximately half that of the control spring 466. However, ~ince the outlet valve must alway~ stand up to a higher pressure than the inlet valve, the additional spring 474, in this embodiment a helical compres~ion spring, mu~t be adjusted higher by a force corresponding to the pre~sure differential Qp (Fig.3) than the force required for closing the inlet valve 422.
Operation:-In the neutral po~ition the inlet valve 422 i~closed and tha outlet valve 424 opened. If during a steering movement the tappet 470 moves to the right (a~
viewed in Fig~5), the cup springs 472 are streqsed, w~ile the control ~pring 466 i3 expanded. When the force S
(Fig.3) has been exceeded, the outlet valve 424 closes.
When the limit force G is reached, the forc~ exerted on the valve member 428 holds the balance to the supply pressure. When the limit force G has been exceeded, the inlet valve 422 opens. Pressure fluid can flow from the ~upply connection 403 into the pres~ure cham~er 420 and huild up in it a pre~sure whose ~alue depends on the actuating force exerted at the steering wheel. As a result the piston 448 is moved to the right, ~o that it follow~ the movement initiated by the tappet 470.
When the tappet 470, actuated from the steering wheel, has moved far enough to the right for a collar 469 of the ~top pin 468 to abut the balance beam 464, the force of control ~prin~ ~66 is rendered ineffective.
The cutting-off point A ~Fig.3) :i~ reached. The inlet seated valve 422 open~, so that the full accumulator pre~sure can have effect in the working chamber 420.
The outlet valve 424 remains closed. Its additional ~pring 474 is able to hold the balance to the full accumulator pressure.
After the cutting-o~ point A has been exceeded, no appreciable ~urther travel of the tappet 470 in relation to the piston 448 i8 requir~d - i.e., nor any further stres~ing of the centring springs 472 - for a further adjustment o~ the steered wheels. The further steering movement therefore is effected without any appreciable further increa3e in the actuating force at the steering wheel ~even thou~h accompanied by further rotation of the ~teering wheel).
Rack and pinion steering gear.
Fig~5 shows a rack and pinion ~teering gear with two pairs of seated valve~ 522, 524 and 522', 524' each having one balance beam 564, 564', in an arrangement qimilar to the embodiment illustrated in Fig.4~ The tappet 570 is rigidly connected to the rack 540. The rack has t~Yo centring sprin~s 572, 572'. The tappet 570 actuates via two control spring3 566, 566` the two balance beams 564, 564'. No separate pins corresponding to the pin 468 in Fig.4 are provided. End stops for control springs 566, 566' are in this embodiment formed by collars 569, 569' of the tappet 570.
In this embodiment the outlet seated valve 524 haq an additional -~pring 574 in the form of a compres~ion spring, and the balance beam 564 actuates the valve me~ber via a projection 576. The same applie to the right-hand outlet valve 524'.
The supply connection 503 and the return connection 5S8 are connected via ducts 503', 558' to the seat of the right-hand inlet valve 522' and the outlet chamber of the right-hand outlet valve 524'.
Operation is the same as in the embodiment illus-trated in Fig.4~

Embodiments with balance beam in a pre~ure-relieved chamber.
In the em~odiments illu~trated in Figs . 4 and 5 the balance beam and the member~ 468 and partly 470 used for ita actuation are accommodated in the working chambers of the adjusting motor. A~ a result the control mechanism i~ located in the pressure chamber~, and this is prefer-ably to be avoided.
In the embodiment illustrated in Figs~6 and 6A a balance bea~ 606 is accommodated in a chamber 610 ~hich is open towardR reservoir 608 - i.e., is pressure-relieved - and i8 arranged between a hollow cylindr1cal casingl612 to be attached to the vehicle and a cylindrical member 614 which i~ di~posed rotatably, but axially non-displaceable, in casing 612. The member 614 i~ in one piece with pinion 616 which engages in a rack (not ~hown).
~ne member 614 is sealed by means of four annular seals 618 in relation to the casing 612 and ha~ thrae annular ~rooves 620, 621A, 621s, of which the annula~ groove 620 is connected via ~upply connection 603 ~o pressura accumulator 604, while the two annular grooves 620A,520B
are c~nnected to the two working chambers 623A,623B o~
the adju~ting motor. The cylindrical memb~r 614 is formed with six longitudinal ducts 625A,625B,626A,626~, and 627A,627B. The annular groove 620 connected to the pressure source is connected ~ia the two longitudinal ducts 625A,625B to the supply chambers of the twv inlet valves 631A,631B. The working chamber 623A of the adjust-ing motor is connected via annular groove 621A and longi-tudinal ducts 626A, 627A to the valve seat of the outlet valve 62~A and the spring chamber of the inlet valve 631A. Correspondingly, the workin~ chamber 623B of the adjustin~ motor i9 connected via annular groove 621B and longitudinal ducts 6268, 627B to the seat of the outlet valve 629B and the spring chamber of the inlet valve 631B.
The two inlet valves are constructed in the same manner as pre~sure-relieved valves. Only the left-hand inlet valve as ~hown in Fig.6a will ~e de~cribed. A
piston 637A on who~e pi~ton rod 635A a valve member 633A
is arranged iB accommodated fluid-tight in a ~alve bore 632A. The effective cro~-sectional areas of the piston and the valve seat are e~ual to one another. There i3 high pre~sure inside the valve bore 632A, but it acts in a similar manner on the pistom and valve member~
In this case an additional spring 639A in the form of a helical compres~ion ~pring i~ arranged in the inlet v~lve. It maintainq the valve closed and provideq the necessary differential pres3ure ~p or hysteresis.
A sh~ft 641 is driven from the steering wheel (not shown) via a ~teerin~ spindle. The shaft 641 is connected for co-rotation via a forked member 643 to one end of a torsion rod 645 whose other end is attached for co-rotation in cylindrical memk~r 6140 l`he forXed member 643 ~ears via two control ~prings .

647~,647B, which also act a centring springs, against the lower end of the balance beam 606, as viewed in Fig.6a. The pistons 637A,637B are diqposed on both ~ides in the centre of the balance beam, and the valve merrbers 649A,649B o~ the outlet valve~ are diqposed at the top end of the balance beam 606.
The cro~-sectional areas of the piston~ 637A, 637B are twice as large as the ~eat cros~-sectional areas of the outlet valves 629A,629B., The balance beam 606 haq identical length~ between the outlet and inlet valves and the place~ of engagement of the control spring~ 647A,647B~
Conqe~uently the control springs exert on the inlet valve~
twice a~ great a force as on the outlet valves.
Operation:-When the shaft 641 i s ~o rotated from the steeringwheel again~t a resistance of the steered wheels that the forked member 643 (Fig.6a) i 9 moved to the right, the balance beam 606 under the influence of the control qpring 647B and additional spring 639B, clo~e3 the out-let valve 629B and relieves the inlet seated valve 631B.
When the limit force has been axceeded, the inlet valve act~ as a pressure balance and controls in the proport-ional range the pre~sure in the adjusting motor w~rking chamber 623B, which then con~titutes the presqure chamber.
With a further increa~e of the force on the steering wheel beyond the cutting~off point ~, a mechanical stop is produced between the forked member 643 and the balance -2~-beam 606. The inlet valve 631B i~ opened by the result-ing travel control. The full pressure can then have effect in the adju3ting motor preqsure chamber. Working fluid can in each case flow away fro~ the pres~ure-relieved working chamber, in this embodiment 623A, of the adjusting motor through the relieved outlet valve 629A into the reservoir 608.
The embodiment illu~trated in Fig.7 differ~ ~rom that illustrated in Fig.S by the featur~ that the rack 701 and the two balance beams 703, 703' are accommodated in a pressure-relieved chamber 70~ and ~y the fact that the two balance bea~s are constructed as resilient 5trip9.
In acc'ordance with the embodiment illustrated in Figs,6 and 6a pressure-relieved inlet seated valves 707 etc.
are provided. Only the left-hand side of the arrange-ment tas viewed in Fig.7) will be described hereina~ter.
The right-hand side is a mirror-image thereof. A stepped piston 710 is ~lidably guided in a worXing cylinder 709, The stepped piston 710 i9 qealed in relation to the cylinder wall by two annular ~eals 712 and 713 at both -ends of a working chamber 715. The piston 710 has a ~upply line 716 which is at high pre~sure and extends to ~he inlet seated valve 707. The inlet seated val~e 707 has a valve member 717 which i~ connected via a thrust rod 718 to a fluid tightIy guided piston 720.
An a~ditional or hy~ter~si~ spring 722 which bears against a radial projection 724 o~ the stepped piston 710 3q~

~s--acts on the valve member 717~
The balance beam 703 i~ incorporated in a ~top rocker 726. The central portion of the ~top rocker b~ars via centring springs 728 against the stepped piston 710.
The two end~ 730 of the ~top rocker constitute ~tops for the end3 of the balance beam in the cutting-off zone.
The two stepped pistons 710,710' are rigidly inter-connected by a push-and-pull rod 731. The rack 701 i~
1idably guided in the longitudinal directio~ on the push-and-pull rod 731 and engages a pinion 732 actuatable from the ~teering wheel.
In the neutral position illustrated both ends o~
the rack 701 bear against the balance beam 703,703' under the force of the two centring springs 728,728'. The centring spring~ and the balance beams co-operate to form the control springs. Otherwise l:he operation of the v~lves is 3ubstantially identical to that described hereinbefore with reference to Fig~. 6 and 6a.
Hydro~tatic -eteering sy~te~.
Fig.8 shows the application of the inventiQn to a hydro~tatic steering sy~tem - i.e., a ~teering sy~tem in which there i~ a hydraulic connection, but no continuou~
me~hanical connection, between the steering wheel and ~he ~eered vehicle parts~
A manual and metering pump 803 - i.e~, a pump which in normal operatiQn acts merely as a metering or apportion-ing pump for the pressure fluid coming from a pres~ure source, in this embodiment a pressure accumulator 804, and acts as a manual pump only when pressure fails, is driven from steering wheel 801. The pump 803 has a mechanical output in the form of a pivotable arm 806 on which two centring springs 808 act.
Adjusting motor 810 is supplied via grooves 812A, 812B of an axial piston valve 814 whose piston 816 can be adjusted by the arm 806.
Two identical, pressure-balanced inlet seated valves 818A, 818B are provided the supply chambers of which are connected to a constant pressure source, in this embodi-ment the pressure accumulator 804. Only the left-hand valve will be described. Its piston 819A has a stop pin 821A which is enclosed by a control spring 820A. The control spring is operative in the proportional zone between the inlet valve 818A and the piston 816 of the axial piston valve. At the end of the control zone, namely at the cutting-off point A, the inlet valve 818A
is entrained by the piston 816 via the stop pin 821A and the valve is opened by travel control. In this embodiment also an additional spring 822A is provided for the purpose described hereinbefore. The outlets of the inlet seated valves are connected via lines 824A, 824B to the two connections of the pump 803. Branch lines 826A, 826B
extend to two separate cylinder chambers of the axial piston valve 814. The central cylinder chamber is connected to reservoir 828.

Operation:-In the neutral position the pres~ure source 804 i9fluid-tightly sealed off by the two inlet seated valves 818A, 818~ so that no flow los~es occur.
When the ~teering wheel 801 i~ rotated, a differ-ential pressure build~ up vla the pump 803. Let it be a3~umed that delivery is in the direction indicated by the arrow~ Preq~ure fluid can flow in through the inlet valve 818A but not out from the line 824B. Consequently the arm 806 i5 e~trained and pusheq the valve piston 816 to the left (as viewed in the Figure). A~ a result a flow path is opened up via a pair of control edges 830~
to the working chamber 832~ o~ the adjusting motor. The working chamber 832~ i~ relieved via a pair of control edges 834A to the reservoir 828.
At the same time a force is exerted on the control ~prin~ 820A from valve pi~ton 816. After the limit ~orce G has been exc~eded, inlet valve 818A operates in the proportionality zone and build~ up a pres~ure in the line 824Ao If a higher pres~ure is required in the working chamber 832B than wa~ produced manually in the line 824B, the inlet valve 818A ensure~ a pres~ure increase with an only alightly increa~ing pressure gradient via t~e pump 803 (in thi~ pha~e the pump is driven as a motor), Suitable adaptation to one another of the additional ~prings 822A, 822B, whi~h act as hy~teresi~ springs, en~ures that the system is first o~ all charged at the start of a steering movement which is exerted on the steering wheel from the neutral position. A pressure i5 then produced at ir~ on the intake side of the manual and metering pump ~ i~e., assuming a steering movement of the ~ame direction, at first exclusively in line 824A, before pressure fluid can flow away on the delivery side -i.e., from line 826B, since then the pairs of control edges 830B and/or 834A are still clo~ed.
After a predetermined force on the steering wheel has been exceeded, the steering system operates as des-cribed hereinbefore in the cutting-off zone.
The driving force for the c:ontrol springs can be picked up on the primary side (st:eering wheel side) of the steering transmission, as shown in Figs~6 and 6a.
Instead of this, it can be pickecl up on the secondary side of the steering tran~mission, as shown by Figs.2, 5 and 7.

Claims (12)

The embodiments of the invention in which an exclu-sive property or privilege is claimed are defined as follows:-

1. A hydraulically operated steering system particu-larly for vehicles, comprising an actuating means and an adjusting motor, having two working chambers, for the steered vehicle parts, working fluid supply lines which extend from a pressure source respectively to the working chambers of the adjusting motor and contain two inlet seated valves closed in the neutral position of the steering system, and return flow lines which extend respectively from the working chambers of said motor to a reservoir and contain two outlet valves, the two inlet seated valves being operatively connected via control springs to the actuating means for transmitting a valve operating force in opposite directional senses to the respective inlet valve in response to displace-ment of the actuating means from the neutral position, whereby a regulated pressure proportional to the valve operating force is established in one of the operating chambers to which pressurised fluid is conducted by one of the inlet valves.

2 A steering system as claimed in claim 1, wherein the two outlet valves are spring-loaded seated valves which are connected via their control springs in opposite directions to the actuating means, the inlet and outlet valves belonging to the same working chamber of the adjusting motor are connected in opposite direc-tions to the actuating means, and in the pressure con-trol zone of the inlet valve the outlet valve connected to the pressure chamber of the adjusting motor holds the balance to a pressure greater by a differential pressure .DELTA.p than the inlet valve associated with the same pressure chamber.

3. A steering system as claimed in claim 1, wherein the inlet seated valves are so pressure-balanced that forces acting on the valve member are independent of the pressure operative in the supply connection, and the control spring and an additional spring acts in opposite directions on the valve member, the additional spring being the decisive factor in maintaining the differential pressure .DELTA.p.

4. A steering system as claimed in claim 3, wherein the inlet valve member is connected to a piston which slides fluid-tightly in an associated valve bore and whose operative cross-sectional area is equal to the valve cross-sectional area, and the supply connection discharges into the valve bore between the valve member and the piston.

5. A steering system as claimed in claim 1, wherein a balance beam or two balance beams disposed in oppo-site directions actuate the two pairs of valves associated with the working chambers; the associated control springs are disposed between the actuating means and the or each balance beam; the or each balance beam is non-positively connected to the valve members of the inlet and outlet valves; and additional springs are provided to produce the differential pressure between the or each balance beam and the associated valve members.

6. A steering system as claimed in claim 5, wherein provided between the actuating means and the balance beam is a mechanical lost motion connection whose lost motion zone so corresponds to the working zone of the control spring that, when the lost motion has been used up, the balance beam opens or releases for opening the inlet valve for the unimpeded flow of pressurised fluid into the pressure chamber of the adjusting motor.

7. A steering system as claimed in claim 6, wherein after the lost motion connection has been used up - i.e., the cutting-off point has been exceeded, the balance beam is inoperative, and the additional spring associated with the outlet valve stands up to the full pressure of the pressure source.

8. A steering system as claimed in claim 6, wherein after the lost motion connection has been used up -i.e., after the cutting-off point has been exceeded, the balance beam or a stop rocker forms a non-positive connection between the actuating means, the inlet and the outlet valve, and the inlet valve opens constrainedly against the force of its additional spring and maintains the outlet valve closed against the full pressure of the pressure source.

9. A steering system as claimed in claim 8, wherein the balance beam is constructed as a resilient strip which, after the lost motion has been used up, is rendered inoperative by stops or entraining elements.

10. A steering system as claimed in claim 1, wherein in a hydrostatic steering system a manual and metering pump drivable by the actuating means is connected down-stream to the inlet seated valve, the said pump having a mechanical output which actuates a piston valve; the piston valve performs inter alia the function of outlet valves; and the control springs are non-positively connected to a movable part of the piston valve.

11. A steering system as claimed in claim 10, wherein the piston valve also has a supply valve connected down-stream of the pump, to the adjusting motor.

12. A steering valve arrangement for use in a hydrauli-cally operated steering system, comprising supply lines which extend from a pressure source respectively to the working chambers of an adjusting motor and contain two inlet seated valves closed in the neutral position of the steering system, and return flow lines which extend res-pectively from the working chambers of said motor to a reservoir and contain two outlet valves, the two inlet seated valves being operatively connected via control springs to an actuating means of the steering system for transmitting a valve operating force in opposite direc-tional senses to the respective inlet valves in response to displacement of the actuating means from the neutral position, whereby a regulated pressure proportional to the valve operating force is established in one of the operating chambers to which pressurised fluid is con-ducted by one of the inlet valves.