DD145388A5 - STEERING VALVE FOR A HYDRAULIC OPERATED STEERING SYSTEM WITH CLOSED CENTER - Google Patents

Description

/ g jj% $ ίώ? ίί / 55 665 17

Steering valve for a hydraulically operated steering system with a closed center

Field of application of the invention

The invention relates to a steering valve with a closed center 5 in which the inlet of a pressure "quölle is closed in lieutralstellung _e Such a 'steering valve has compared to an open center, which requires a constant Heut raid urehlauf the flow agent, the advantage that less energy is consumed when not operated steering because of the lack of circulation losses.

Such steering valves are to be used mainly in hydraulic steering systems, ie those in which there is a mechanical connection between the actuator (steering wheel) and a servomotor for the vehicle parts to be steered. Here, hydraulic assistance is only required for driving on the lefthand, but not for driving straight ahead, for example on motorways, so that considerable energy savings can be achieved when driving straight ahead ο

The invention is also applicable to hydrostatic steering systems, ie those in which a mechanical connection between actuator and servomotor is not present. Vehicles equipped in this way are admittedly not approved for high speeds »Here, however, an energy loss due to circulation of the fluid should be avoided if a certain steering angle remains unchanged, for example, when an engine

? nf7 -jί.ρο. ,, ςϊ oi / _s β ο

2o 11. 1979 55 665 17

«J J- - 2

working machine with unchanged steering angle, in rune or in motion, carried out work

Characteristic of the known technical solutions

Steering valves referred to in the preamble of claim 1 are known from DE-OS 21 31 276 and 24- 46 841. In the known steering valves, the intake valves, which are components of the steering valves, designed as seat valves and are closed in neutral position. There will be no circulation losses. If the actuating device is deflected beyond the response, the one seat valve is opened and a working pressure builds up in one of the working chambers of the servomotor, namely the respective pressure chamber. This is ensured by a special design of the inlet seat valves that a proportional to the working pressure reaction force is exerted on the seat valves ₉ which is noticeable on the actuator (the steering wheel) and the driver negotiated the required steering feel

On steering stop after exhaustion of the response, one or the other of the inlet poppet valves opens due to mechanical stop, ie sudden connection of the actuator to the valve. This causes sudden and excessive pressure fluid in the respective pressure chamber. * The result is a discontinuity in ani enkvor gang, which could not be eliminated with such steering valves bislier.

11. 1979 665 17

A steering valve of another type with inlet seat valves is also known from the DB-AS 12 14 554 (Bosch) »This steering valve works on the pressure reducer principle and requires a complex construction *

"Object of the invention"

The aim of the invention is to avoid the loss of energy when driving straight ahead or unchanged steering angle or «the high design cost»

Presentation of the

Object of the present invention is a steering valve with inlet Sitzv.entilen form such that the TJ _n continuity occurs during the Anlenkvorgang, but the advantage of a proportional reaction from the pressure chamber should be retained on the actuator

The invention uses a different principle to control the inlet seat valves than in the prior art (technology, namely a pure force control.) This is achieved by arranging the already required actuation springs of the inlet seat valves in the course of the steering linkage in such a way that the The seat valve begins to open when a predetermined force, the so-called limit force, has been reached "In the pressure chamber of the servo motor, after the force has been exceeded, the pressure can rise but only build steadily so that no

2 * 11. 1979 55 665 17

Discontinuity in the Anlenkvorgang can occur _e The springs of the inlet poppet valves in the adjoining proportional range (that is in the range of steering angles, in which on the actuator a working pressure proportional reaction force is felt) the effect of control springs for the pressure relief valves working inlet -Sitzventile "

For the principle of the invention, it is irrelevant »whether a power transmission to the Eegelfedern tapped directly from a steering shaft, a part of a steering gear or a part following the steering gear

By the steering valves j which are known from the above-mentioned two DE-OS., Although in neutral position of the steering a passage of fluid prevented «In contrast, however, fluid must flow constantly when the driver when driving straight on a sloping to one side road must constantly draw against something or crosswind _e Then one of the intake is necessarily open -Sitzventile? and again flow losses occur ",

According to a further development of the invention according to claim, the two exhaust valves are designed as seat valves and actuated by their Eegelfedern of the actuator ,, This has the advantage that even when 'overcoming the limit force when pressure medium via the one inlet valve for Stel! Motor passes , a leakage to the. Expansion tank is prevented »Will that

2 * 11. 1979 55 665 17

Steering wheel with force only held, but not rotated »so no pressure medium is consumed. This concerns the case of a crosswind or sideways inclined penalty,

Another advantage of the development according spoke 2 is that "at least each pair of valves (a working space associated inlet» and exhaust valve) can be actuated by one and the same component of the actuator, if it is gesorgj according to claim 2, that the exhaust valve always one by one Pressure difference greater pressure holds the balance than the associated inlet valve.

The operation of the valves is so easy. This advantage is achieved by using pure force control also for the actuation of the exhaust valves ",

In the simplest case, the spring chambers of inlet and / tuslaß seat valve are connected to the associated working space of the servomotor. As a result, the force control of these valves in a space that is under working pressure must intervene · In a development of the invention according to claim 3, this can be avoided by using pressure-balanced inlet seat valves, such that the forces acting on the valve body forces are independent from the pressure acting in the inlet connection and that the regulating element and an auxiliary spring act in opposite directions on the valve body, which is decisive for the maintenance of the pressure difference / p ',

• 2 «11. 1979 55-665 17

The valve body is advantageously connected to a piston which is guided in a corresponding valve bore under sealing and whose effective cross section is equal to the valve cross section and the inlet port opens between the valve body and the ΚοΓ-ben in the valve bore _β The force control for these valves can then in to be accommodated in a pressure-relieved room *

If inlet and outlet seat valves are equipped with separate control springs, it may be difficult to ensure that both valves maintain balance within the whole range of proportionality and that they differ by a certain pressure difference. This difficulty can be found in a further development 5 thereby avoid »that for the actuation of the two pairs of the working space associated valves a balance beam or two counter-mounted balance beam serve» that the associated control springs between the actuator and the or the balance beam are arranged, that or the balance beam in frictional connection with the valve bodies are the intake and exhaust valves and that are arranged to achieve the pressure difference between the or the balance beam and the associated Ventilkorρerη auxiliary springs «It then acts a common control spring up intake and exhaust valve wähisnd an additional spring ensures that the pressure difference in the range of proportionality is maintained. _B Thus, the stiffnesses of two springs and the seat cross-sections of two valves of each pair do not need to be narrower

2 · 11. 1979 55 665 17

214. J ^ J - ⁷ -

Tolerances to be matched.

Beyond a certain size of steering angles, they are exceeded when parking "a proportional reaction to the actuator is no longer required, however, desired that the maximum working pressure in the respective pressure chamber of the servomotor is available" It should occur the so-called cut-off effect means the proportionality line is cut off. After reaching the AbschneidepunJctes should be without significant increase in o.uf the actuator force applied the working pressure take its maximum value. »To achieve this, in the above-mentioned steering valves according to the DE-OS quite a considerable construction effort required» There must be two additional Steering limiting valves are provided "In the case of the above-mentioned DT ~ AS 12 14-554, the cut-off effect is not achievable at all",

By a development of Erfindimg according to claim 6, the cut-off effect _t when using a balance beam, in a very Einfädler way achievable, namely by the fact that between the actuator and the balance beam a mechanical lost motion connection is provided, the lost motion range corresponds to the working range of the control spring, so in that, after exhausting the lost motion, the balance beam opens or opens the inlet valve for the unimpeded inflow of pressure fluid into the pressure chamber of the servomotor.

It is also advantageous that after the exhaustion of the backlash connection, that is, exceeding the Ab-

- 8th -

2. 11. 1979 665 17

cutting point, the balance beam is ineffective and the additional valve associated with the auxiliary spring the full pressure of the Dr uekquelle withstood *

It may also be appropriate that after the exhaustion of CQotgangverbindung, that is, exceeding the cut-off point, the balance beam or a stop rocker forms a positive connection between actuator, intake and exhaust valve, the intake valve against the force of its auxiliary spring forcibly opens and the exhaust valve against the full pressure of the pressure source keeps closed.

Is advantageous. the balance beam formed as a leaf spring, which becomes ineffective after exhausting the backlash by stops or drivers «

In the context of a hydrostatic steering, the inlet seat valve is advantageously followed by a nand- and metering pump which can be driven by the actuator. The pump has a mechanical output which serves to actuate a slide valve. The slide valve has, inter alia, the function of outlet valves and the control springs in frictional connection with a movable cable of the slide valve ·

The slide valve then advantageously also has one of the H + D pump naclige switching et it inlet valve to the servomotor on _a

2 » 11 _e 1979 55 665 17

ff mi ^ i? _M Q "

Execution sb e ispiel

Embodiments of the invention are explained below with reference to the drawings © It zeigens

Fig, Is the principle of force control,

Fig. 2 s highly schematic part of a steering system with two pairs of intake and Auslaßsitzventilen, which are controlled together _s

Fig β 3 * in a graph the various steering ranges,

Fig. 4 is a longitudinal section through an embodiment of the invention with balance beam through which a pair of poppet valves are controlled;

FIG »5s a similar embodiment of the invention, _e incorporated in a rack and pinion steering"

Figure "6 and 6a: in longitudinal section ο cross section respectively along the line aa in Fig _e 6, a further embodiment of the invention, in which on the primary

 'S

side of a steering gear a common scale bar serves to control two pairs of intake and exhaust valves ₉

Fig. 7s part of a rack and pinion steering, in which at the · secondary side of the steering gear control valve according to another embodiment _v's of the invention with a leaf spring-like Libra

«10 -

2. 11. 1979 55 665 17

'# efiP% # ·' IU

bars are provided ₄

FIG. 8 shows a further embodiment of the invention applied to a hydrostatic steering system. FIG.

Fig. 1 shows a Sinlaß-seat valve 2, which is arranged in a feed line 3; , which leads from a pressure accumulator 4 to the one working space of a servo motor, not shown. The inlet «seat valve 2 has a valve ball 6 and a valve seat 8« The closing or control spring 10 is seated between the valve ball 6 and a part 12 »in mechanical drive connection with the actuator, the steering wheel" stands. In general, the actuator has a separate centering device »which is schematically indicated here by the springs 14.» However, the puncture of the centering device can also be adopted by two control springs arranged in opposite directions · On the opposite side of the part 12 is again the same valve arrangement to think » The spring chamber of each of these inlet Sitζventile is connected to one of the working spaces of the servomotor The valve has the function of a pressure relief valve. Depending on the operation of the part 12, it sets the appropriate working pressure in the pressure chamber of the servo motor »The centering springs 14, which are shown here as helical compression springs _s are realized because of the small travel in a known manner more suitable as a bending rod, torsion bar or disc springs *

Function?

The electric spring 10 ₈ the return springs 14 and the Ven-

- 11 -

2o 11 «, 1979 55 655 17

I 733

tilquerschnitt are coordinated so that they hold in neutral position, when the actuator is free of force, a balance that is slightly larger than the pressure prevailing in ZuIaufanschius 3 memory pressure »This is in the neutral position of Zulaufan ~ closed safely closed» Will the part 12 to the right, adjusted, so by relaxation of the Eegelfeder 10 decreases the force acting from the right on the valve ball 6, until finally the ruling in ZuIaufanschius 3 pressure overcomes the spring force and lifts the valve ball 6 from its seat. Then, pressure fluid from the accumulator 4- in the pressure chamber of the servomotor reach the differential pressure between pressure accumulator and pressure chamber of the servomotor is held by the Eegelfeder. After a limit force has been exceeded by the actuator _t is proportionality ZYiischen the operating force F and the working pressure ρ in the respective pressure chamber of the servomotor. Fig * 3 shows this Zusammenhängeβ When a steering angle of O forth remains the pressure ρ in the first servomotor O, until the limit force is reached G "Then, the pressure increases ρ is proportional to the applied force F on the steering wheel along the line 16 to _e

The limit force is certainly desirable in vehicle steering, as one likes to dispense with the hydraulic support in the area of small steering angles and steering forces to improve the road contact ».

B _e in exceeding the limit force is obtained a smooth transition, because by placing the control spring between the BetätigungsGinrichtung and this Ventilkörp3r

2. 11. 1979 665 17

1 1 If # «<». - 12 -

gradually opens according to the increase in the operating force. The lack of rigid connection between the actuator and the valve body also has the advantage that a poppet valve can also be used as an outlet valve, which is not possible for reasons of production in a rigid connection.

Fig. 2 shows the basic structure of a steering with pure seat valve control. Each of the working spaces 20 "20 * of the servomotor 21 is associated with a pair of valves, so the working space 20, an inlet seat valve 22 and an outlet seat valve 24. The same applies to the working space 20 '. The components in the right half of the figure bear the same reference numerals, but with apostrophe ..- provided »As far as the arrangement is symmetrical, details are described only to the left half of the drawing. They apply analogously to the right half. The inlet seat valve 22 has as a control spring 26 a compression spring which presses its valve body 28 against the valve seat 30. The outlet seat valve 24 has a conical spring 32 in the form of a tension spring which engages the valve body 34 corresponding deflection against his seat 36 pulls. The outer ends of the springs 26 and 32 are secured to a rigid, tong-like shaped portion 38 of the actuator. The part 38 has a rack 40 which is adjustable by a rotatable from the steering wheel ago pinion 42 in the direction of the double arrow 44 «

The piston rod 46 and the piston 48 of the Sbellmotors are fixedly arranged on the vehicle, while the cylinder housing 50 is movable relative to them. The

- 13 -

2. 11. 1979 55 665 17

*. 13 ».

Valve seats 30 and 36 are rigidly connected to the cylinder housing of the servomotor The spring chambers of the control springs 26 and 32 open into the working space 20, which is shown schematically here by lines 52 and 53

The inlet ports 3 »3 ^{1 of} the inlet seat valves are connected to the pressure accumulator 4« A common return port 58 of both outlet seat valves is connected to the expansion tank 59 *

A special centering device was used here, since the control springs 26; 32 and so on * with appropriate dimensioning this function can take over *

In the neutral position ₈ shown in Fig. 2 in which the operating member 38 is free of force, the inlet valves 22 and 22 ^{f are} closed * They are set to a pressure j etvias is higher than the pressure prevailing in the pressure accumulator 4 * Both exhaust valves 24 _s 2M- ^f are open Both work spaces 20 _$ 20 ^{5 of} the servomotor are depressurized «,

If the operating part 38 is displaced to the right by turning the steering wheel via the pinion 42, the control springs of this movement counteract a resistance which can be felt on the steering handwheel _e As soon as the limit force G (FIG. 3) is reached after a certain displacement Regelfeder 26 ', as far as relaxed _s that prevailing in the pressure accumulator 4 pressure overcomes the spring force and that pressure fluid into the working space 20 ^f ,

«14 -

2 _β 11. 1979 55 665 17

which is now Druckraura, can flow. Tor reaching this state, the outlet seat valve 24 'has closed and its control spring 32 ^f was tensioned. Inlet and exhaust valves are matched to one another so that the exhaust valves always maintain a balance which is greater by a pressure difference ρρ than the pressure which at the same time holds the inlet valves in balance. As a result, at no operating position of the steering fluid pressure medium, which is to be supplied to the pressure chamber of the servomotor, flow out of the outlet valve connected to it «

B _e i the considered movement of the operating part 38 to the right, the elastic spring 32 of the outlet seat valve 24, which is connected to the pressure-relieved working space 20, relaxed, so that the working fluid can flow out here for Ausgleichst © holder 59 »The inlet seat valve 22nd remained closed in this whole process

While pressure builds up in the pressure space 20 ^f , which is equal to the accumulator pressure minus the pressure gradient at the intake valve 22, the cylinder housing 50 of the servomotor _{e is} displaced. The rigid connection of the valve seats to the housing results in a control circuit which produces the Cylinder housing the actuating part 38 nachzuführen _e

In Fig. 3, the straight line 16 shows the conditions at the respective working inlet-seat valve, namely the pressure ρ which it adjusts in dependence on the actuating force F exerted on the steering handwheel. As mentioned, the associated outlet seat valve holds one each

- 15 -

2 _e 11. 1979 55 665 17

the pressure difference Äp higher pressure the balance. For the outlet valve results in the straight line 60, which, as shown here, "runs parallel to the straight line in the ideal case. In no case may both lines intersect. This would mean that the inlet and outlet. Are. The same side are open at the same time, so that pressure fluid could flow from the memory, bypassing the servo motor directly to the expansion tank. If, on the other hand, both lines always have a distance Ap, namely a safety whirlpool that in principle can be freely selected, then the pressure fluid must always travel through the servomotor., The straight line 60 intersects the F axis at the point S _e The distance 0 - S represents the Increase in the operating force within the play of the spring 24- ^{f of} the exhaust valve _a

If the steering is not actuated by the steering wheel but by the steered wheels, for example in the return from cornering in the straight ahead, and the actuator is in or near its neutral position (between 0 and S in Fig "3), so are both exhaust valves 24-, 24 '' open, and there is an unobstructed working fluid circuit between the working spaces of the servomotor and the expansion tank. The cylinder housing 50 and the steered vehicle wheels can thus move unhindered in both directions.

The driver is not completely free after a turn the steering wheel, but he lets it run back slowly with slowing down, the operating part 38th

- 16 -

2. 11 · 1979 55 665 17

~ 16 «

from its reached extreme position, z. If, for example, the lever is moved to the left on the right, then the force of the regulating spring 26 * of the inlet valve increases, and the inlet of the pressure vessel 4 is shut off, If the actuating force has been reduced by a value ΔF that corresponds to the pressure difference / dp corresponds, the exhaust valve 24 opens ^! ₉ and hydraulic fluid can flow to the expansion tank »In the further course of the control spring 32 * 'is relaxed, and with further outflow of hydraulic fluid from the pressure chamber 20', the pressure drops at the outlet valve» 'The straight line 60 to Pig * 3 is in the direction of arrow, So, down, go through, until finally the point S is reached and the work spaces are depressurized. Even with the return process, the pressure in the pressure chamber of the servomotor is clearly assigned to a force on the steering wheel.

'Beyond a certain force on the steering wheel is not interested in a further proportional increase in the power »Especially during parking a greater increase in steering power is undesirable. At the same time, however, one is not interested in a feedback of the forces acting on the wheels * The proportionality range, which is represented by the straight line 16 in Pige 3, should be cut off beyond an actuating force A. Without appreciable increase in the actuation force, the pressure ρ in the pressure chamber then increases steeply along the straight line 62 to ₀ (the straight part 16a was cut off),

Leaves in a steering valve according to the present invention

- 17 -

11 »1979 665 17

*. 17 ~

the cut-off effect very simply realize that the effect of the control springs of a certain actuation path and thus a certain actuation force is canceled. This is shown in the following example.

In the embodiments of FIGS. 4 and 5 are previously treated components with the same two-digit reference \ vie previously designated »but preceded by 4 or 5» so that result in hundreds of signs »

4 shows the cylinder housing 450 of the servomotor s its piston 443 with a piston seal 477 and a piston rod 479 _e. Accordingly, only the left half of this piston also shows only a pair of seat valves, namely the inlet seat valve 422 and the outlet »Poppet valve 424 * In the right half of the piston, the same valve arrangement has to be considered again. All four valves are thus integrated in the piston. In order to avoid difficulties in the coordination of the valve springs to each other, here each an inlet and an outlet valve by a balance beam 464 are operated together. The inlet valve 422 does not have its own control spring. Rather, both valves are actuated via a common control spring 466 arranged in the middle of the balance beam. This control spring surrounds an Alischlagbolzen 468 _β The actuator acts on a plunger 470 centered with the aid of Te-llerfeder 472

*. 18 -

2 * 11. 1979 55 665 17

The control spring 466 acts on the balance beam 464 with equal forces on the inlet valve 422 as well as on the outlet valve 424 * To neutral position, when the inlet valve 422 is closed, the exhaust valve 424 hold force-free au, an additional spring 474 is required «their bias etvia half is as large as that of the Rege If eder 466. Since the exhaust valve but always withstand a higher pressure than the inlet valve, the auxiliary spring 474, here a helical compression spring must be set higher by one of the pressure difference A, ρ according to FIG as the force required to close the intake valve 422.

In the neutral position, the inlet valve 422 is closed and the outlet valve 424 is open. "If the plunger 470 is moved to the right when the steering angle is steered, the cup springs 472 are tensioned while the control spring 466 is released. 3) closes the outlet valve 424. Upon reaching the limit force G, the force exerted on the valve body 428 the inlet pressure keeps the balance, after exceeding the limit force G opens the inlet valve 422. Pressure fluid can flow from the inlet port 403 into the pressure chamber 420 and there build up a pressure whose magnitude depends on the force exerted on the steering handwheel, thereby moving the piston 448 to the right to follow the movement initiated by the plunger 470,

H _a t the plunger 4-70, operated by the steering wheel forth, moved so far to the right that a collar 469 abuts the stop pin on the beam 464, as is the

- 19 -

2. 11, 1979 55 665 17

- «8 βΐτ <Ä

Δ $ S <3> - 19 ~

Control spring 466 ineffective »The cut-off point A (FIG. 3) is reached. D _a s inlet seat valve 422 opens so that the full accumulator pressure can affect the working space 4-20. The outlet valve 424 and the outflow channel 458 remain closed, its auxiliary spring 474 is able _s the full storage pressure to balance the »

After exceeding the cut-off point A no further significant YJeg of the plunger 470 against the piston 448 longer required for a further adjustment of the steered wheels, so no further tension of the centering springs 472. The further wheel drive thus takes place without appreciable further increase the operating force on the steering wheel (although with further rotation of the Lenkhaidrades).

FIG. 5 shows a rack-and-pinion steering system with two pairs of seat valves each having one balance beam in an arrangement similar to the embodiment according to FIG. 4. The slide 5JO is fixedly connected to the rack 540. The rack has two centering springs 572 and 572 ^f . The plunger actuates two balance beams 564 and 564 * via two control springs 566 and 566 ^f . There are no special bolts according to the bolt 468 shown in FIG. 4 here. "End stops for the control springs 566 and 566 'are formed here by collars 569 and 569 ^{f of} the plunger 570.

The outlet seat valve 524 has one here. Zusatzfedör 574 in the form of a compression spring, and the balance beam 564 actuates the valve body via an extension 576. The same applies to the right outlet valve.

- 20 -

2V. 11. 1979 55 665 17

33 -20

The ZuJ. to the chi uß 503 and the return connected 558 are connected by channels 5O3 ^f and 558 »with the seat of the right inlet valve 522 ^s and the discharge chamber of the right outlet valve 524 ^f «

The mode of action is the same as in the embodiment according to FIG. 4 *

In the embodiments according to Pig * 4 and 5, the balance beam and serving parts 468 and partly 470 etc * are housed in the working spaces of the servomotor.

In the embodiment according to FIGS. 6 and 6a, the Y / Aage bar 606 is accommodated in a space 610 which is opened against the compensating container 608 and which is located between a hollow cylindrical housing 612 to be fastened to the vehicle and a rotatable therein. but immovably arranged cylindrical portion 614 is located. The part 614 is integrally formed with the pinion 616, which engages in the rack, not shown here. The part 614 is sealed by means of four ring seals 618 relative to the housing 612 and has three annular grooves 620, 62IA and 621B, of which the annular groove 620 via the inlet port 6O3 communicates with the accumulator 604 while the two annular grooves 621A and B communicate with the two working spaces 623A and B, respectively, of the servomotor. The cylindrical portion 614 includes six longitudinal channels 625A and B,

- 21 -

· 2 · 11. 1979 5.5 665 .17

626A and B and 627A and B. The annular groove 620 communicating with the pressure source is connected to the inlet spaces of the two inlet valves 631A and B through the two longitudinal channels 625A and B, respectively. The working space 623A of the servomotor is connected through the annular groove 621A and the longitudinal passages 626A and 627A to the valve seat of the exhaust valve 629A and the spring space of the intake valve 63IA, respectively.

Accordingly, the working space 623B of the servomotor is connected to the seat of the exhaust valve 629B and the spring space of the intake valve 63IB via the annular groove 621B and the longitudinal oil passages 626B and 627B, respectively.

The beid.en inlet valves are designed in the same way as pressure-relieved valves. Only the left-hand valve is described in FIG. 6a. A piston 637A is accommodated in a valve bore 632A with a seal, against which piston rod 635A the valve *, body 633 ^ · sits. The effective cross-section of the piston and the valve seat glebhen * Within the valve bore 632A there is high pressure, but acting on the piston and valve body in the same way.

In this case, a Z _u is set spring 639 A arranged in the form of a Schraubendruckfedör at the inlet valve * keeps the valve closed and provides the necessary pressure difference / ipoder hysteresis.

From the steering handwheel, a 1 / VeIIe 641 is driven via the steering spindle. It is over a forked part

  - 22 -

2 _β 11. 1979 665 17

643 rotatably connected to the one end of a torsion bar 645, whose other end is non-rotatably mounted in the cylindrical part 614.

By fork-like part 643 is supported by two Shelf springs 647A and B, which also have the effect of Zentrierfüfern, at the in Fig. 6a lower end of the balance beam 606 abe In the middle of the balance beam on either side of the piston 637A and B on, and at the upper end of the balance beam, the ytil bodies 649A and B of the exhaust valves.

The cross-sections of the pistons 637A and B are twice as large as the seat cross-sections of the exhaust valves 629A and B _e. The balance beam has equal lengths between exhaust and intake valves and will attack the control springs 647A and B ". As a result, the control springs exert twice as great on the intake valves Power like on the exhaust valves «

If the shaft 641 is rotated from the steering wheel counter to a resistance of the steered wheels so that the fork-like portion 643 moves to the right in Fig. 6a, the balance beam closes and relieves the discharge valve 629B under the influence of the control spring 647B and the auxiliary spring 639B Inlet seat valve 631B. After exceeding the limit force, this inlet valve works as a pressure compensator and regulates the proportional pressure in the now forming the pressure chamber Arbeitsimm 623B of .Stellmotors. With further increase of the force on the steering wheel beyond the cutting point A etnsteht a me- ·

~ 23 -

2. 11. 1979 55 665 17

* · 23 -

mechanical stop between the fork-like part 643 and the balance beam 606 _β . The path control created thereby opens the inlet valve 631B. The full pressure can now affect the pressure chamber of the servomotor. Working fluid can in each case flow out of the pressure-relieved working space, in this example 623A, of the servomotor, through the unloaded outlet valve 629A into the expansion tank 608.

The embodiment of Fig. 7 differs from that of Fig. 5 in that the rack 701 and the two balance beams 703 and 703 ^f are housed in a pressure-relieved space 705 and in that the two balance beams are formed as leaf springs. 6 and 6a, pressure-relieved inlet seat valves 707, etc. are described below, only the left-hand side of the arrangement will be described, the right-hand side mirror-inverted "In the working cylinder 709, a stepped piston 710 is displaceably guided It is sealed against the cylinder wall by two sealing gaskets 712 and 713 on either side of the one working chamber 715. The piston has a high pressure inlet line 716 which carries inlet valve seat 707. This valve has a valve body 717 via the push rod 718 is connected to the sealing-guided piston 720 «

On the valve body 717, the additional or hysteresis spring 722 acts, which is supported on an extension 724 of the stepped piston.

The balance beam 703 is inserted in a stop rocker 726.

2. 11. 1979 55 655 17

adds »The middle part of the stop rocker is supported by centering springs 728 on the stepped piston. The two ends 730 of the stop rocker form stops for the ends of the balance beam in the cut-off area ·

The two stepped pistons 710 and 710 ^f are connected by a push-pull rod 731 rigidly · The rack 701 is guided displaceably in the longitudinal direction on this push-pull rod. It engages with the pinion 732 which can be activated by the Lenldiandrad. * -

In the illustrated Keutalstellung both ends of the rack 701 on the balance beam 703 and 703 ^f under the influence of the two centering springs 728 and 728 'on *. These centering springs and the balance beams together form the control springs. Otherwise, the function of the valves 707; 734; 734 'is substantially the same as described above with reference to FIGS. 6 and 6a.

8 shows the application of the invention to a hydrostatic steering d _e h .. on a steering in which a hydraulic _s but no continuous mechanical connection between the steering wheel and steered vehicle parts be available _β

From the steering wheel 801 a hand and dosing pump 803 (HiD pump) is driven, d * h _e a pump that in normal operation only as dosing or Zumeßpumpe for from a pressure source, here a pressure accumulator 804,

- 25 ~

2. 11 ·· 1979 55 665 17

originating pressure fluid acts and only in case of pressure failure as a hand pump. The H + D pump 803 has a mechanical output in the form of a pivotable arm 806 »acting on the z. Ei centering springs 808»

The servomotor 810 is fed via servomotors 812A and B of an axial piston valve 814, the piston 816 of which is adjustable by the arm 806 _a

There are two equal, pressure-balanced inlet seat valves 818A and B are provided, the inlet spaces with a constant pressure source, here a pressure accumulator 804, in communication. Only the left valve will be described. Its piston 819A has a stop pin 821A surrounded by a control spring 820A. The control spring is effective in the proportional range between the intake valve 818A and the piston 816 of the AxiaL piston valve. At the end of the control range, at the cut-off point A, the inlet valve 818A is entrained by the stop pin 821A from the piston 816 and the valve is opened by travel control. In addition, an auxiliary spring 822A is again provided for the purpose described above. The outlets of the inlet poppet valves communicate via lines 824A and B with the two ports of the H + D pump 803. Branch lines 826A and B lead to two separate cylinder chambers of the axial piston valve 814-. The central cylinder chamber is connected to the surge tank 828.

In the neutral position, the drubk source is hermetically sealed by the two inlet seat valves 818A and B,

- 26 -

2. 11. 1979 55 665 17

So there are no flow losses ",

If the Lenkliandrad 801 is rotated, a differential pressure is built up via the H + D pump 803. It is assumed that is conveyed in the direction of the arrows. Drip fluid may flow through the inlet valve 818A, but not drain from line 824-B. As a result, the arm 806 is entrained and pushes the valve piston 816 to the left. As a result, a flow path is released via a pair of control edges 83OB to the working space 832B of the servomotor. The working space 832A is relieved via a pair of control edges 834-A to the surge tank. At the same time, a force is applied to the control spring 820A from the valve piston 816. The inlet valve 818A operates upon exceeding the limit force G in the range of proportionality and establishes a pressure in line 824A. If a higher pressure is required in the working space 832B than it does by hand in line 824B

when applied, "the 818A inlet valve causes a pressure increase with only a slight increase in the pressure gradient across the H + D-Puspe 8Ο3 (the H + D pump is driven as a motor in this phase).

By appropriate adjustment of the additional springs 822A and B1 have the puncture of hysteresis, can ensure that at the beginning of a steering movement, which is exerted from the neutral position out on the steering wheel, the system is initially charged. It then arises first on the suction side of the H-s-D pump "d. lio (assuming a steering lock of the same calibration) initially only in line 824-A a pressure before

- 27 -

2. 11. 1979 55 665 17

the pressure side, ie from line 826B, pressure fluid can flow, since then the control edge pairs 83OB and / or 834-A still, are closed.

After a certain force has been exerted on the steering handwheel, the steering works as described above in the screeine range

The driving force for the control springs can be tapped on the primary side (steering handwheel side) of the steering gear, as shown in FIGS. 6 and 6a. Instead, it can be tapped on the secondary side of the steering gear ₍ as shown in FIGS. 2, 5 and 7),

- 28 -

Claims (3)

2o 11. 1979 55 665 17 Steering valve for a hydraulically operated steering system with a closed center, which comprises an actuating device and a control motor for the steered vehicle parts, as well as lines leading from a pressure source to the servos of the servomotor and containing two inlet seat valves closed in itfeixtral position and return lines; which lead from the working noise to a surge tank and contain outlet valves, characterized in that the two inlet seat valves (22; 22 'uswe) via springs ("control springs" 26, uswe) in opposite directions with the actuator (381 ^ -70 uswe ) are connected _e Steering valve according to point 1, characterized in that the two exhaust valves (24; 629; 734-, etc.) seat valves are _t via their springs ( "control Federn" 32 ξ 466; 64 ?; 703; 728, etc.) opposite to the actuating device (38; 470; 634; uswe) are connected, that in the same working space of the servomotor associated intake and exhaust valves (22; 24; 631A _S 629A, 707, 734, etc.) are connected in opposite directions with the actuator-and that in the pressure control range of the intake valve, the exhaust port connected to the Bruckraum of the servomotor - 2.9 - 2 · 11 «1979 55 665 17 214 «29 - Valve a pressure greater by a pressure difference Δ ρ pressure the scale cold than the same pressure chamber to parent inlet valves Steering valve according to item 1 or 2, characterized in that the inlet seat valves (631; 707 j 818 US ^ e) are pressure balanced, such that forces acting on the valve body are independent of the pressure acting in the inlet port and that on the valve body in opposite directions the control spring (647; 7035 728; 820, etc.) and an auxiliary spring (639; 722; 822, etc.) acting to maintain the pressure differential; A ρ authoritative Steering valve according to point 3t characterized by,. in that the valve body is connected to a piston (637; 720 usvn) which. in an associated valve bore is guided under sealing and whose effective cross section is equal to the valve cross section =, and that the Zulaufanschius between the valve body and the piston opens into the Ventilbohrimg. Steering valve according to one of the preceding points, characterized in that allocated to the actuation of the two pairs of the working raumen valves (e.g. 522, 524,. 621A; 629A on the one hand, 522 '; 524 ^f; 621B; 629B on the other hand) a balance beam (606 ) or two balance beams arranged in opposite directions (2 "B ₀ 564; 564 ¹ ) serve to ensure that the associated control springs (566; 566 ^f ; 647A; 647B) are located between the actuating elements. a * 11 * 1979 55 665 17 Jl is ca κι λλ direction (570) and the or the balance beam are arranged »that the one or more balance beam in frictional connection with the valve bodies dsr inlet and outlet valves and that to achieve the pressure difference between the or the balance beam and the associated valve bodies auxiliary springs (eg. 639A) « 6 »Steering valve according to point 5 * characterized in that between the actuator and the balance beam a mechanical dead band connection is provided, the backlash range corresponds to the working range of the control spring» such that the balance bar after exhausting the backlash the inlet valve for unimpeded inflow of hydraulic fluid in the Pressure chamber of the servomotor opens or releases to open (FIGS. 4 to 8). 7 »Steering valve according to item 6, characterized in that after the exhaustion of the backlash connection, that is to say exceeding the cut-off point $, the balance beam (4-64; 564; 564 ') is ineffective and the auxiliary spring (474j 574; 574') associated with the outlet valve withstand the full pressure of the pressure source · 8 »Steering valve according to point 6 _S characterized in that after the exhaustion of the lost motion connection, that is, exceeding the cut-off point, the balance beam (606) or a stop rib (726) forms a frictional connection between actuator, inlet valve outlet valve, the inlet valve - 31 - 2. 11. 1979 665 17 against the force of its auxiliary spring (639; 722) forcibly opens and keep the exhaust valve closed against the full pressure of the pressure source 9 * Steering valve according to item 8, characterized in that the balance beam is formed as a leaf spring (703), which after exhausting the backlash by stops (73O) or driver ineffective vard « 10c Steering valve according to point 1, characterized in that in the context of a hydrostatic steering the inlet seat valves (818) downstream of a driven by the actuator ago hand and metering pump (HiD pump 8O3) is followed, which has a mechanical output (806), serving to actuate a spool valve (8Ή), the spool valve inter alia having the function of exhaust valves (834-) and the control springs (820) being in frictional engagement with a movable part (816) of the spool valve. 11 »steering valve according to item 10, characterized in that the slide valve (814)" also each one of the H + D pump (8O3) downstream inlet valve (830) to the servomotor »