DE2526391A1 - SERVO MOTOR - Google Patents

Description

S e r ν ο m 2526391 Patent attorneys
° & ^ρ ρ £ ϊ JJ: £ _h ^u *
DipJ, Ipq p · f ^ 8 Munich 2
Mo2artstr. 23 File number M 3554 June 11, 1975 0 t 0 r The Bendix Corporation Executive offices Bendix Center Southfield, Me. 4Ro75, United States

The invention relates to a servo motor, in particular for a vehicle brake system.

Wherein in the US-PS servomotor described 3,599,406 concentric delivery piston disposed in the master cylinder portion that provide an increased output pressure when the required braking force exceeds that value, the pressure difference generated by a force acting on a partition in the servo motor, by means of a vacuum source is achievable. The concentric delivery pistons are adjusted jointly by the pressure difference generated in the servomotor until the working force that can be achieved by the negative pressure is fully exhausted, whereupon one delivery piston becomes independent as a function of a manual input force

509882/0713

adjusted by other delivery pistons and the main cylinder section applied with an additional actuating force. However, the additional actuation force acts both on the first than on the second concentric delivery piston, thereby reducing the effect of the operator to be applied, manual input force is reduced, since the Counterforce of the delivery piston must first be overcome by the input force before the output pressure of the master cylinder section increases.

According to the invention, a servomotor is to be created in which an increase in the amount of the feed piston arrangement, in particular the master cylinder section, without a corresponding increase in that of the operator input force to be applied is possible.

For this purpose, the invention also provides a servomotor a working section which has a working piston acted upon by a differential pressure and controlled by an input force; a hydraulic conveying section with a conveying piston arrangement which is slidably arranged in a housing bore and is coupled to the working piston, which is characterized is by a control device actuated as a function of the input force, through which the effective piston area the delivery piston arrangement and the actuating force generated by the pressure difference on the working piston

509882/0713

cut reduced effective cross-section of the conveyor basket assembly is transferable.

In the case of the servomotor according to the invention, the actuating force generated by the pressure difference on the working piston is reduced from a greater to a reduced level under certain operating conditions Removed piston surface of the delivery piston assembly.

In another advantageous embodiment of the invention it is recommended that the housing bore be stepped and have a section of enlarged diameter and a section of reduced diameter which can be connected to a consumer via an outlet opening is that the advancing piston arrangement has a piston surface of larger diameter arranged in the enlarged bore section to delimit a first pressure chamber and a venting chamber that can be connected to a hydraulic accumulator and a piston surface of smaller diameter arranged in the narrower bore section to delimit a second one Has pressure chamber that channels are formed in the delivery piston assembly through which the first with the second Pressure chamber can be connected via a first valve and the first pressure chamber can be connected to the ventilation chamber via a second valve is that the second valve is an actuator depending on the one hand on the input force and on other

509882/0713

252S331

on the other hand from an oppositely acting, from the fluid pressure Closing force generated in the first pressure chamber can be adjusted and by the closing force in a first operating mode is held in the closed position until the input force the closing force exceeds and, in a second operating mode, the pressure in the first pressure chamber exceeds the second Valve is reducible, and that by a switching device for the first valve, a fluid flow from the second in-the first pressure chamber is prevented during the second operating mode.

Further details and features of the invention emerge from the remaining claims and the following description in conjunction with the drawings. Show it:

1 shows a schematic representation of a servo brake system with one designed according to the invention Servo motor;

Fig. 2 shows a modified embodiment of the servo motor the brake system according to FIG. 1;

3 shows a further modified embodiment

the servo motor of the brake system according to FIG. 1;

509882/0713

4th 2526391
- 5 - Fig. a third modified embodiment of the servomotor of the braking system according to 5 Fig. 1; Fig. a diagram showing the relationship between the servomotor ge from the operator according to Fig. 1 supplied input force and the delivery pressure delivered by the servomotor shows, where the abscissa is the input force 6th and the ordinate indicates the outlet pressure; Fig. a schematic representation of a servo brake system with a section shown th servomotor according to a second embodiment 7th example of the invention; Fig. a schematic representation of a servo brake system with an in section darge set servo motor according to another off 8th exemplary embodiment of the invention; and Fig. a modified version of the servo motor according to FIG. 7.
- 6 -

509882/0713

According to Pig. 1, the brake system 10 contains a pressure medium servomotor with a hydraulic conveyor section 14, which the front wheel brakes 16 and the rear wheel brakes 18 as a function acted upon by an input force exerted on the pedal 20 by the operator with a hydraulic actuating force.

The pressure medium servo motor includes an operating section 12

/ which through with a first housing shell 22, a winding terminal 26 is connected to a second housing shell 24. A working piston in the form of a movable partition 28 is arranged in the first and second housing shells 22 and 24 and delimits a first and a second variable volume Chamber 30 and 32. The partition wall 28 is provided with a central hub 34 on which a reinforcement plate 36 is attached via finger 38. A membrane 40 is on the outer edge with a first bead 42 between the flap 44 and the splash 46 of the first or second housing shell 22, 24 held and placed with a second bead 48 in a snap fit on the lip 50 of the reinforcement plate 36.

The hub 34 extends with a rearward extension 52 through an opening 54 in the first housing shell 22. The extension 52 has an axial bore 5S _f in which a servo control valve arrangement 58 is arranged, which is connected by the pedal 20 via the push rod 60 to the input valve.

509882/0713

force is applied.

The control valve assembly 58 includes a vacuum plate valve 62 and an atmospheric pressure poppet valve 64 _c at a caused by the push rod 60 of a movement S are actuated Hiebers 66 sequentially.

The vacuum poppet valve 62 includes a valve surface 68, which has a flexible portion 72 of a stationary Bead 70 is kept at a distance. The bead 70 is supported by a holder 74 surrounding the push rod 60 secured in the axial bore 56. The valve surface 68 is held against a vacuum channel by a first spring 76 80 geLegatien vacuum valve seat 78 pressed. The vacuum channel 80 connects the first chamber 30 with the Axial bore 56 of hub 34.

The atmospheric pressure poppet valve 64 includes a cylindrical portion 82 which is defined by a plurality of lugs 84 in the axial bore 56 is positioned. The lugs 84 drive a first atmospheric pressure valve seat 86 into contact with the valve surface 68. An annular extension 88 extends inwardly from the cylindrical extension 52 to the push rod 60. The extension 88 forms on its one side a second atmospheric pressure valve seat 90, which is through a between the holder 74 and the push rod 60 arranged spring 94 against a

509882/0713

rear extension 92 of the slide 66 is pressed. Another spring 96, which lies between the holder 74 and a plate 98, serves to reset and press a web 100 of the slide 66 against a shoulder 102 of the hub 34. A return spring 104 located in the second housing shell 24 acts on the hub 34 and The membrane 40 presses against buffers 106, which are arranged on the housing shell 22. In this position, the negative pressure that reaches the first chamber 30 from the intake pipe of the vehicle via the check valve 108 sucks the air in the second chamber 32 via a duct 110 into the axial bore 56 and from there via the negative pressure channel 80 and the partition 28 is kept in equilibrium by the negative pressure.

The hydraulic conveying section 14 contains the area converter 112 described below:

A delivery piston assembly 114 is connected to the hub 34 via a Screw connection 116 fastened until the end 118 is attached to a Shoulder 120 abuts. The piston assembly 114 is stepped and includes a piston surface 122 of larger diameter, those in an enlarged bore section 124 a stepped bore 126 and a piston surface 128 of smaller diameter, which extends into a reduced section 130 of the bore 126 on the average. One Lip seal 132 on the larger lateral surface 122 of the Piston assembly 114 divides the extended - 9 -

509882/0 713

Bore section 124 in a first pressure chamber 134 and a vent chamber 136. The enlarged bore section 124 is provided with first and second openings 138 and 141 extending through the housing 142, the first pressure chamber 134 or the venting chamber mib a fluid reservoir 144 connects. A lip seal 138 prevents fluid communication to a second pressure chamber 146 along the diameter smaller piston area 128. In the piston assembly 114 is an axial channel 151 is formed. A first radial channel 152 connects the first pressure chamber 134 with one in the axial channel 151 located inner chamber 176, while a second radial channel 154, the ventilation chamber 136 with the axial channel 151 connects.

A first valve 156, which consists of a valve disk 158 with a plunger 160, which is pressed by a spring 164 against a pin 162, controls the connection between the first pressure chamber 134 and the second pressure chamber 146 over the axial channel 151. An actuating device 166 with a cylindrical section 168 which is attached to a counter disk 170 is attached to a sleeve 172 which, in this embodiment, the switching device 148 for the first valve 156 forms. A seal 174 is in the axial channel 151 on an enlarged portion of the sleeve 172

- 10 509882/0713

arranged and prevents fluid communication between the interior chamber 176 and the second pressure chamber along the axial channel 151. An axial bore 178 is formed in the sleeve 172, which the tappet 160 of the valve disk 158 gripped with play. The pin 162 penetrates a first and a second slot 180 and 182 in the sleeve 172. A spring 184 urges the cylindrical portion and holds its end face 186 in contact with the washer 170.

A second valve 188 contains a ring plate 190 which is held on a valve seat 192 by a spring 194 is to establish fluid communication between the inner chamber 176 and the vent chamber 136 in a first To prevent operating mode when a force amplification due to a differential pressure acting on the partition wall 28 takes place and the delivery piston assembly 114 is moved into the bore 126.

The second pressure chamber 146 in the hydraulic conveying section 14 supplies the front wheel brakes via an outlet opening 196 16 with hydraulic pressure medium. The conveying section 14 includes a third pressure chamber 198, which is through a Piston 200 is partitioned, which in the narrower bore section 130 by a first spring 202 in the chamber 146 and a second spring 204 positioned in chamber 198

- 11 -

509882/0713

will. The piston 200 is in the narrower bore section 130 during a brake actuation as a function of the actuating movement of the piston arrangement 114 in the direction of a
Expansion of the second pressure chamber 146 for the purpose of equalizing the operating pressure supplied to the wheel brakes is freely movable and at the same time ensures full displacement of the hydraulic medium from the chamber 198 via an opening 206 to the rear wheel brakes 18.

The servo motor works as follows:

When the operator applies an input force to the pedal 20, the push rod 60 moves and allows the valve surface 68 of the vacuum poppet valve 62 to move under the force of the spring 76 to the valve seat 78, whereby the connection of the first chamber 30 with the axial bore 56 via the vacuum channel 80 interrupted
will.

With a further displacement of the push rod 60 lifts
the first valve seat 86 from the valve surface 68, so
that the air located under atmospheric pressure in the axial bore 56 can flow into the second chamber 32 via the channel 110. When air flows into the second
Chamber 32 and negative pressure in the first chamber 30, a pressure

- 12 -

509882/0713

difference that generates an actuating force that is transmitted via the hub 34 to the delivery piston assembly 114 and this is adjusted in the bore 126 of the hydraulic conveying section 14. When adjusting the delivery piston arrangement 114 migrates the larger piston area 122 into the enlarged one Bore section 124 and generates a first hydraulic pressure after the lip seal 132 migrates over the channel 138 Has. This first hydraulic pressure reaches the inner chamber 176 via the channel 152 and then via the Axial bore 178 in the second pressure chamber 146 and from there to the wheel brakes 16. At the same time, the piston is adjusted 200 under the force of spring 202 and the fluid pressure in chamber 146 and creates a corresponding one Hydraulic pressure in the chamber 198 for actuating the rear wheel brakes 18.

The first hydraulic pressure in the chamber 176 acts on the cylindrical section 168 and balances the input force which is transmitted to the counter disk 170 via the cylindrical web of the slide 66. When the operator increases the input force via the push rod 60, the pressure difference applied to the partition wall 28 increases. accordingly, until the second chamber 32 is completely filled with air under atmospheric pressure, which is commonly referred to as "vacuum exhaustion". This is described below as the first operating mode of the 3 servo

- 13 -

509882/0713

motors ". In the second operating mode of the servo motor every additional input force applied by the operator is transmitted from the slide 66 via the washer 170 and displaces the cylindrical section 168 against the force of the spring 184 in the direction of the end face 208 of the Valve disk 158 of the first valve 156. When the sleeve 172 is shifted in the axial bore 151, the expands Spring 194 extends while spring 164 is compressed and the end face 208 presses against the sleeve 172, whereby the fluid communication between the inner chamber 176 and the second pressure chamber 146 is interrupted. With a further increase in input force, the shoulder becomes 210 of the actuating device 166 for the second valve 188 applied to the annular valve disk 190, whereby the communication between the inner chamber 176 and the vent chamber 136 is released. In the open position of the second valve 188, the fluid pressure in the first pressure chamber 134 is due to the possibility of evasion dismantled to the ventilation chamber I36, so that the through the Differential pressure generated operating force acting via the hub 34 on a delivery piston of reduced usable area is transferred, i.e. to the second piston surface 128 of reduced diameter, which is further into the second pressure chamber 146 is inserted, with the result that the wheel brakes 16 and 18 are subjected to an increased hydraulic pressure will. A controlled reduction in the first hydraulic

- 14 -

509882/0713

pressure in chamber 134 to the pressure value of the venting core I36 can thus reduce the pressure caused by the pressure difference at the Partition 28 generated operating force from the piston surface 122 of enlarged diameter can be switched to the piston surface 128 of smaller diameter, so that a stepped working brake booster is created in the form of a servomotor for the brake system, the output pressure of which controlled by the input force exerted by the operator.

Point 137 on curve 139 in Pig. 5 shows the switchover the first to the second mode of operation when the pistons on both sides of the counter disk 170 have the same diameter. This gives a smooth transition and means that the braking system is working in a state of equilibrium. By change the diameter of either the piston-shaped section 168 or the piston-shaped section 101 for consideration Characteristic curve 141 or characteristic curve 143 results from operating parameters of the brake system. Like point 145 shows the slope of the first or the second operating stage depending on the nature of the relationship of the input force be shifted to the output force to be corrected operating parameters.

In the housing 142 there is an outlet 212 which connects the inlet of the bore 126 with the atmosphere in order to

- 15 -

509882/0713

allow hydraulic fluid possibly adhering to the surface 214 and penetration thereof To prevent hydraulic medium in the front chamber 30 of the working section 12 of the servo motor.

In the exemplary embodiments according to FIGS. 2, 3 and 4 are those corresponding to the embodiment according to FIG Components are not identified by reference numbers if they are arranged in the same place in the servomotor.

The surface modifier 112 according to FIG. 2 is the same as in FIG Fig. 1, wherein the change in the pressure-generating surfaces in the counterpressure device 220 takes place, via which the hydraulic Conveyor section 14 generated pressure is conveyed to the operator via the push rod 60.

The counter-pressure device 220 gives the operator a mechanical braking feeling with the aid of several radially extending ones Levers 222 which are arranged at the bottom of a bore 228 on the end 224 of the slide 66. The cylindrical one Piston section 168 of actuating device 166 acts with the levers 222 together and generates a control force that in the first operating mode that in the first pressure chamber 134 generated fluid pressure and in the second operating mode the flow generated in the second pressure chamber I46

- 16 -

509882/0713

indicates medium pressure. A lip seal 226 prevents pressure medium from penetrating into the counter-pressure device during operation of the servomotor. When the vacuum is ^{exhausted 11} , the end 224 of the slide 66 hits the cylindrical piston section 168j, whereby the first valve 156 is closed and the second valve 138 is opened one after the other, so that the controlled switching of the operating force from the first, larger piston surface 122 to the second, smaller piston area 128 takes place.

In the embodiment according to Pig. 3 is the actuator 366 is firmly coupled to the slide 66 via an adjustable connection 368. The first valve 356 includes a cylindrical valve body 350, which is arranged in the axial channel 351 and fixed to the plunger 362 of the actuating device 366 is connected. A lip seal is located on the outer surface of the cylindrical valve body 350 358, which is a fluid connection from the axial passage 151 prevented in the inner control chamber 376. The second valve 388 includes one that is resiliently pressed against a valve seat 392 Valve disk 390 which, in the closed position, establishes a connection between the control chamber 376 and the venting chamber 336 prevented.

In the case of a "negative pressure exhaustion" in working section 312 the slide 366 is under the influence of the operator

- 17 -

509882/0713

man applied input force so adjusted that one after the other, the seal '358 moves past the channel 352, the connection from the first pressure chamber 534 via the axial channel 351 is closed and the connection via the second valve 388 is opened. When the shoulder 374 on the annular Valve disk 390 hits, the hydraulic pressure generated during the first mode of operation is a function of the the input force exerted on the brake pedal 20 is reduced in a controlled manner. When the input force disappears, the actuator 366 reset in the axial channel 151 under the action of the return spring 96, so that the negative pressure in the chamber 30 can suck the air out of the chamber 32.

j In the embodiment according to Fig. 4, the actuating

transmission device 466 a first sleeve 472, which is in the axial ; channel 151 next to a shoulder 474 in the control chamber 476 j is arranged ^. In the first sleeve 472 is an axial ! Bore 478 is formed, which forms a flow path from the control chamber 476 into the second pressure chamber 446. One j Spring 480 presses the first sleeve 472 into contact with the annular valve disk 490. A second, in the control chamber 476 arranged sleeve 482 forms a guide surface for an actuation piston 484. The valve disc 490 is adjacent to the end of the second sleeve 482. The actuation piston 484 includes a first cylindrical end portion

- 18 509882/0713

488, which rests axially in alignment with the head 400 of the slide 66 on the G-pressure disc. At the end 492 of the actuating cage 484 there is a valve ball 486 which interacts with a Sit25 494 of the first sleeve 472.

If in the embodiment according to Pig. 4 the operating point of the "vacuum exhaustion" occurs, the on The input force exerted by the slide 66 is transmitted directly via the counter-pressure disk 470 and adjusts the Actuating piston 484 in the control chamber 476. The valve ball 486 sits on the valve seat 494 and the spring 480. presses the first sleeve 472 firmly against the actuating piston 484, so that the connection between the control chamber 476 and chamber 446 is interrupted. When the spring 480 is compressed as a result of the actuating movement of the actuating piston 484 is, the end 496 lifts from the second valve disk 490, so that the hydraulic pressure in the first Pressure chamber 434 can correspondingly decrease as a result of the connection to the ventilation chamber 436. With a decrease of the first hydraulic pressure in the chamber 434, the piston assembly 114 is adjusted under the action of The operating force exerted by the pressure differential across the hub 34 and sets the fluid in the chamber 446 through the smaller piston area 428 moving in the second bore section 430 under pressure, creating an increased outlet pressure for actuating the wheel brakes in the brake system 10

- 19 -

509882/0713

generated v / ird.

When the input force disappears or decreases, it acts on the valve ball in the second chamber 446 486 acting fluid pressure means a displacement of the actuating piston 484 against the counter-pressure disk 470 and together with the spring 480 a movement of the first sleeve 472 against the annular valve disk 490, whereby the connection between the control chamber 476 and the venting chamber 436 is interrupted. As the hydraulic fluid in the first pressure chamber 434 is at a reduced pressure value, the hydraulic pressure in the second Hydraulic chamber 446 rapidly reduced to a value approximating the original first fluid pressure. When the return spring 96 moves the slide 66 further into the release position, the vacuum valve 62 prevents again an inflow of air into the second housing chamber 32, so that the negative pressure in the housing chamber 30 a Can cause negative pressure equalization on the partition wall 28.

- 20 -

509882/0713

The braking system 610 according to Pig. 6 contains a hydraulic servo motor 612 with a hydraulic conveying section for supplying the front wheel brakes 616 and the rear wheel brakes 618 with a hydraulic actuation force depending on the force applied by an operator to the Brake pedal 620 applied input force.

The fluid servo motor 612 has an operating section with a first housing shell 622, which is connected to a second housing section 624 via a winding terminal 626 is. A working piston in the form of a movable partition wall 628 is located in the first and second housing shells 622, 624 and delimits a first variable volume chamber 630 and a second variable volume chamber 632. The partition wall 628 is provided with a central hub 634 to which a reinforcement plate 636 is secured by fingers attached. A membrane 640 is on the outer edge by a first bead 642 between a flange 644 and a Flange 646 of the first and second housing shells 622 and 624 held and seated with a second bead 648 in the Snap fit on lip 650 of reinforcement plate 636.

The hub 634 includes a rearward extension 652, which extends through an opening 654 in the second housing shell

509882/0713

624 extends. An axial bore 656 is formed in the extension 652 in which a servo control valve arrangement 658 is arranged to be acted upon by an input force exerted by the pedal 620 via a push rod 660.

The control valve assembly 658 includes a vacuum poppet valve 662 and an atmospheric pressure poppet valve 664, the are actuated one after the other when the slide 666 is moved by the push rod 660.

The vacuum poppet valve 662 is provided with a bead fixed by a flexible portion 672 670 separate valve surface 668 provided. The bead is 67O secured in the axial bore 656 by a holder 674 encompassing the push rod 660. A first spring 676 presses the valve surface 668 against a valve seat 678 located next to a vacuum channel 680. The vacuum channel 680 connects the first housing chamber 630 with the axial bore 656 of the hub 634.

The atmospheric pressure poppet valve 664 includes a cylindrical portion 682 which is formed by a plurality of tabs 684 in the Axial bore 656 is positioned. The tabs 684 abut a first atmospheric pressure valve seat 686 the valve surface 668. An annular extension 688 runs from the cylindrical extension inward to the thrust

- 22 -

509882/071 3

rod 660. The approach 688 forms on its one side a second atmospheric pressure Yentilsitz 690, the through a spring 694 located between the holder 674 and the push rod 660 against a rearward extension of the slide 666 is pressed. A second spring 696 is located between the holder 674 and a plate 698, which is used to reset and press a web 700 on the slide 666 against a snap ring 702 in the hub 634. One Return spring 704 located in the housing shell 622, which acts on the hub 634, presses it into the buffer 706 the housing shell 624. In the position shown, the Any negative pressure carried from the intake pipe of the vehicle via a check valve into the first housing chamber 63O Air in the second housing chamber 632 via the channel 710 into the axial bore 656 and via the channel 680, so that there is negative pressure equilibrium at the partition wall 628.

The hydraulic conveying section 624 contains the area converter 712 described below:

The area transducer 712 is provided with a central piston 714 on which an annular piston 732 is slidably arranged. The central piston 714 is attached to the hub 634 and extends through a section 7ί6 which is enlarged in diameter a bore 720 in a bore section 718 smaller

- 23 509882/071 3

Diameter. The central piston 714 is penetrated by an axial channel 722. Via a first radial channel 724 and a Second radial channel 726, the axial channel 722 is connected to the enlarged bore section 716. Between the First radial channel 724 and the second radial channel 726 there is an inner chamber 728. A first shoulder 730 forms a first stop for the annular piston 752, which is concentric to the central piston 714 on its lateral surface 734 'is stored. A snap ring 736 limits the movability of the annular piston 732 on the lateral surface 734. The annular piston 732 divides the enlarged bore section 716 into a pressure chamber 738 and a venting chamber 740. One arranged in the venting chamber 740, with The spring 742 connected to the central piston 714 presses the annular piston 732 against the shoulder 730, whereby a connection between the ventilation chamber 740 and the memory 744 via the opening 746 is ensured. At the same time the Pressure chamber 738 with the memory 744 via the opening 748 in connection.

The valve ball 752, which is pressed against a valve seat 754 by a spring 756, is located in the axial channel 722 first valve 750, which the hydraulic connection between the pressure chamber 738 and that between the central piston 714 and the. narrower bore section 718 limited delivery chamber

- 24 509882/0713

758 regulated. The actuation of the first valve 750 is controlled by a switching device 760 which has a through a slot 764 in the central piston 714, has pin 762 attached to ring cage 732. A plunger 766 arranged on pin 762 acts with the valve ball 752 together and keeps it separated from the valve seat 754 when the spring 742 rests the annular piston 732 against the stop 730 holds, whereby an undisturbed connection between the pressure chamber 738 and the delivery chamber 758 is established. In addition to the second radial channel 726, a second valve 768 is arranged in the inner chamber 728, which the connection between the pressure chamber 738 and the venting chamber 740 and has a valve disk 77O, which is controlled by a Spring 774 is pressed against a valve seat 772. The valve disk 770 includes a plunger 775, which is through a Guide surface 776 extends into an actuation chamber 778.

In addition to the guide surface 776, there is an elastic component 780 in the actuation chamber 778.

An actuation device 782 contains an actuation piston 784, which adjoins the axial channel 722 in a Axial bore 786 is arranged. The actuating piston 784 lies with a circular area 788 on the elastic component 780 and is provided with a stepped end 790 that passes through the back pressure disc 792 of the servo motor.

- 25 -

509882/0713

Dichttingen 794 and 796 prevent that in the extended Bore section 716 and hydraulic medium located in the axial channel 722 into the housing 630 of the working section of the servomotor penetrates.

The servo motor according to Fig. 6 works as follows:

When the operator applies input force to the pedal 620, the spring 676, due to the movement of the push rod 660 put the valve surface 668 of the negative pressure valve 662 on the valve seat 678, whereby the connection between the first housing chamber 630 and the axial bore 656 is interrupted via the vacuum channel 680. With another Movement of the push rod 660 separates the first atmospheric pressure valve seat 686 from the valve surface 668 so that the air in the axial bore 656 under atmospheric pressure via the channel 710 into the rear housing chamber 632 can flow in. If there is air in the rear housing chamber 630 negative pressure in the front housing chamber, a pressure difference results at the partition wall 628, which generates an actuating force which is transmitted via the hub 634 is transmitted and pushes the central piston 714 into the bore. At the beginning of the shifting of the central piston If the annular piston 732 moves past the opening 748 under the force of the spring 742, so that hydraulic pressure builds up, which moves undisturbed from the pressure chamber 738 to the conveying

- 26 -

509882/0713

The chamber 758 can propagate and is transmitted via the lines 798 and 799 to the wheel brakes 616 and 618. at an increase in the hydraulic pressure overcomes the force of the spring 742 and that of the working portion of the servomotor The applied actuating force is transmitted to the annular piston 732 via the snap ring 736. When the annular piston 732 moves in the direction of de3 snap ring 736, the plunger 764 is lifted from the "valve ball 752, so that the spring 756 the. Ball 752 counteracts the action of the hydraulic pressure generated in the first operating mode of the servomotor on the valve seat 754 can put.

When the effect of the negative pressure is exhausted, the spring 756 has brought the valve ball 752 onto the seat 754, whereby the connection between the pressure chamber 738 and the delivery chamber 758 is interrupted. Each additional, from Operator input force is applied via the first slide 666 directly to the end 790 of the actuating piston 784 transferred. This additional force leads to the overcoming of the elastic acting as a buffer Component 780 for actuating the plunger 775, whereby the second valve 768 is opened and part of the pressure medium can escape from the chamber 738 via the second radial channel 726 into the venting chamber 740. In the immediate Depending on this change in the hydraulic pressure present in the pressure chamber 738, the shifts

- 27 -

509882/0713

Middle baskets 714 under the action of on the partition 628 attacking pressure difference in the second bore section 718, whereby the hydraulic pressure existing there is increased and the wheel brakes are acted upon in a second operating mode of the servo motor with an increased hydraulic pressure will.

When the input force is reduced, the actuating piston 784 separates from the plunger 775, so that the spring the valve disk 770 can be placed on the valve seat 772, whereby the connection between the pressure chamber 738 and the vent chamber 740 is interrupted. At the same time, the hydraulic pressure in chamber 758 acts on the central piston 714 and the hydraulic pressure in the chamber 758 is reduced to such an extent that the spring 742 pushes the annular piston 732 can apply to the stop 730. When the annular piston 732 approaches the stop 730, the plunger 766 strikes the ball 752 so that the delivery chamber 758 is connected to the pressure chamber 738 and between these chambers Pressure equalization takes place until the annular piston 732 is moved to the snap ring 736 again.

When the input force disappears, the spring 696 pushes the slide 666 against the air poppet valve 664, so that the negative pressure in the chamber 630 air from the chamber 632

- 28 509882/0713

can suction. At the same time, the spring 704 adjusts the Hub 634 to the rear housing shell 624, and since the piston 714 is firmly connected to the hub 634, the stop engages 730 the annular piston 732, whereby the plunger 766 holds the valve ball 752 in the position raised from the seat 754 and the hydraulic medium located in the delivery chamber 758 can escape to the hydraulic accumulator.

The brake system 810 according to FIG. 7 contains a pressure medium servomotor 812 with a hydraulic conveying section 814 for supplying the front wheel brakes 816 and the rear wheel brakes 818 with a hydraulic actuation force depending on an operator acting on the Brake pedal 820 applied input force.

The pressure medium servo motor 812 contains a working section with a first housing shell 822, which has a winding clamp 826 is connected to a second housing shell 824. Sin working piston in the form of a movable partition 828 is arranged in the first and second housing shell 822, 824 and delimits a first, volume-variable Chamber 830 and a second, volume-variable chamber 832. A middle one extends from the partition 828 Hub 834 with a reinforcement plate 836. A membrane 840 is on the outer edge with a first bead 842 between a

/Flange
Flange 844 and one 846 of the first and second housing

- 29 509882/0713

shell 822 or 824 held and with a second bead 048 in a snap fit in one next to the reinforcement plate 836 located groove 850 is used.

The hub 834 extends with a rearwardly protruding extension 852 through an opening 854 in the first Housing shell 822. The extension 852 contains an axial bore 856, in which a servo control valve assembly 858 is arranged to be acted upon by an input force introduced by the pedal 820 via a push rod 860.

The servo control valve assembly 858 includes a poppet valve assembly 862, which is actuated when a slide 866 is displaced by the push rod 860 and successively shuts off the negative pressure and allows an inflow of air in order to avoid a pressure difference at the partition wall 828 to create.

The poppet valve assembly 862 includes a bead 864 separated from a stationary bead 864 by a flexible portion 870 Valve area 868. The bead'864 is in the axial bore secured by a retainer 872 which presses the bead 864 against the extension 852. A first, on one shoulder 880 the spring 874 resting against the push rod 860 presses the valve surface 868 against a next to a vacuum channel 876 lying vacuum valve seat 867. The vacuum channel

- 30 -

509882/0713

connects the first chamber 830 with the axial bore 856 of the hub 834. A second, between the holder 872 and A spring 878 arranged at core 882 of the push rod 860 presses an atmospheric pressure valve seat 884 arranged on the slide 866 in contact with the valve surface 868.

The membrane 840 is provided with buffers by a return spring 888 which is active between the housing shell 822 and the hub 834 890 pressed against the housing shell 824. In the shown Position sucks from the suction pipe via a line 892 past a check valve 893 into the front housing chamber 830 guided negative pressure air from the second variable-volume chamber 832 via a channel 886 into the axial bore 856 and the channel 876, whereby the partition 828 is kept in negative pressure equilibrium.

The hydraulic conveying section 814 contains the area converter 894J described below. The area converter 894 is with a piston arrangement in the form of a stepped cylinder piston 896, which is connected to the hub 854. The stepped piston 896 includes an enlarged diameter Piston section 898, which is arranged in a section 900 of a bore 902 with an enlarged diameter, and a piston section 904 of smaller diameter, which is located in a section 906 of smaller diameter the bore 902 is located. The enlarged piston section

- 31 509882/071 3

893 'divides the enlarged bore section 900 into a pressure chamber 908 and a venting chamber 910. An axial channel 912 passing through the piston 896 has a first Radial channel 914, which connects the pressure chamber 908 with a conveyor chamber 916, and a second radial channel 918, which connects the pressure chamber 908 with the venting chamber 910.

A counter-pressure disk 920, which is arranged in the axial channel 912, is formed by a sleeve protruding from the hub 834 924 held on a shoulder 922. An adjustable extension 927 is attached to the slider 866 at one end and is held at the other end by the sleeve 924 axially in the center of the counter-pressure disk 920. One on the counter pressure disc The switching valve assembly 926 located in 920 regulates the flow of fluid through the axial passage 912. The switching valve assembly 926 is designed similarly to the first and second valves described above with reference to FIG. 4 and provided with a first sleeve 928 which lies adjacent to shoulder 930 in interior chamber 932. An axial hole 934 in the first sleeve 928 forms a flow path from the inner chamber 932 to the delivery chamber 916. A spring 936 presses the first sleeve 928 into contact with an annular valve disk 938. The valve disk 938 is on a second Sleeve 940 attached, which forms a guide surface for an actuating piston 942. The actuating piston 942

- 32 -

509882/0 7 13

lies with its cylindrical end 944 on the counterpressure notch 920 and is directly aligned with the head 946 of the adjustable extension 927. One at the end of the actuating piston 942 arranged valve ball 948 can with an axial bore 934 at the end of the first Sleeve 928 surrounding valve seat 950 cooperate.

The pressure chamber 908 has an opening 952 which lies on a lip seal 954 when the buffer 890 passes through the return spring 888 is held on the housing shell 824, as shown in FIG. In the vent chamber 910, an opening 956 is arranged which is connected to a flow path 958, via which the filling quantity in the Brake system is kept at a constant value by means of the reservoir 960. The hydraulic connection from the reservoir 960 via the flow path 958 is controlled by a tilt valve 962 arranged in a relief chamber 972. The tilt valve 962 includes a valve disc 964 that is attached to

/ is attached to a cylindrical portion 966 of the one The plunger 968 runs through the opening 956 into the venting chamber 910. One located in the vent chamber 972 The spring 970 presses the valve disk 964 onto a valve seat 974. The opening 952 is connected to the valve seat 974 via a channel 976 Relief chamber 972 connected. An axial bore extending through the valve disk 964 into the cylindrical section 966 978 is available via a radial channel 980 with the

- 33 -

509882/0713

load chamber 972 in connection. A valve ball 982 is attached to the axial bore by a spring member 986 enclosing valve seat 984 is pushed to allow fluid flow from the reservoir 960 through the axial bore 978 to prevent. The valve seat 974 is of a first Seal 988 and channel 976 is enclosed by a second seal 990 to ensure that the fluid from the vent chamber 910 via the flow path 958.

The servo motor according to Fig. 7 works as follows:

When the operator applies an input force to the brake pedal 820, the spring 874, as a result of the movement the push rod 860 applies the valve surface 868 of the poppet valve assembly 862 to the vacuum valve seat 867, whereby the communication between the first chamber and the bore 856 via the channel 876 is interrupted. If the push rod 860 is displaced further, the atmospheric pressure valve seat 884 is removed from the valve surface 868 lifted off, so that the air standing under atmospheric pressure in the bore 856 via the channel 836 into the rear housing chamber 832 can flow in. When air flows into the rear housing chamber 832 and negative pressure in the front Housing chamber 830 creates a pressure difference at partition 828. This pressure difference creates a

- 34 -

509882/0713

Actuating force generated, which is transmitted via the hub 834 · the piston 894 is displaced in the bore 902. if the first piston section 898 of the piston 894 is pushed into the first bore section 900, is in the pressure chamber 908 generates a first hydraulic pressure after the lip seal 854 has traversed the opening 952. This The first hydraulic pressure is planted via the channel 914 into the inner chamber 932 and from there via the axial bore 934 in the delivery chamber 916, from where it goes to the wheel brakes 816 got. At the same time, the piston 992 is under the action of the spring 990 and the hydraulic pressure in the chamber 916 acted upon in such a way that a corresponding hydraulic pressure builds up in the chamber 994, which the rear wheel brakes 818 actuated.

The first hydraulic pressure in the inner chamber 932 acts the cylindrical section 944 and is the same as the counterpressure disk 920 via the adjustable extension 927 of the Slider 866 transmitted input force. When the operator increases the input force on the push rod 860, the pressure difference at the partition 828 increases in a corresponding V / eise until the rear housing chamber 832 is completely filled with air under atmospheric pressure, which is commonly referred to as "vacuum exhaustion" will. Any additional input force applied by the operator is transmitted from the slide 866 via the counter-pressure disk 920

- 35 509882/0713

for the purpose of adjusting the actuation piston 94-2. If the adjustment is sufficient, the valve ball 948 is brought onto the seat 950, as a result of which the connection between the pressure chamber 908 and the delivery chamber 916 is interrupted. With a further adjustment of the actuating piston 942, the sleeve 928 is adjusted against the force of the spring 936 and the poppet valve 938 is opened so that the first hydraulic pressure to the venting chamber 910 can be reduced. Since the spring _Λ 970 presses the valve disc 964 onto the seat 974 and the seal 988, the venting chamber 910 is separated from the reservoir 960. When the pressure in the vent chamber 910 exceeds the force of the spring 986, the valve ball 982 lifts off the valve seat 984 so that the fluid can escape to the reservoir 960. At the same time, the differential pressure acting on the partition 828 causes a corresponding movement of the second piston section 904 into the second bore section 906, as a result of which an increased hydraulic pressure is generated in the delivery chamber 916 for actuating the wheel brakes 816 and 818 in the second operating stage of the servo motor.

When the input force disappears, the first piston section engages 898 of the piston arrangement 894, the plunger 968 and opens the venting chamber 910 to the reservoir 960. At the same time sets the return spring 878 the seat 884 on the

- 36 -

509882/0713

Valve surface 868 and lifts it from the vacuum valve seat 367 so that the negative pressure in the housing chamber 830 can vent the rear housing chamber 832, whereby the partition 828 is again held in vacuum equilibrium.

If there is no negative pressure and the operator has to apply the brakes without brake booster, the following workflow results: The first operating mode described above is not carried out correctly because the "Vacuum exhaustion" starts as soon as the servomotor is actuated. As a result of the arrangement of a delay device However, at the beginning of the second operating stage in the pressure chamber 908 in the manner described below the first stage of a two-stage hydraulic pressure can be built up.

The input force exerted on the pedal 820 displaces the push rod 860 so that the slide 866 directly moves the head 946 brings into contact with the counterpressure disk 920. If there is a further shift, the extended one is released Piston portion 898 from plunger 968 and separates the vent chamber 910 from the reservoir 960. In a corresponding manner, this is introduced by the slide 866 via the head 946 Input force the valve ball 948 of the actuating piston 3

brought to the seat 950 and the connection between the. - 37 -

509882/0713

Pressure chamber 908 and delivery chamber 916 closed. At a During a further stroke movement of the piston assembly 894, the fluid located in the pressure chamber 908 is via the inner chamber 932 and channel 918 pushed into vent chamber 910. Since the filling volume of the venting chamber 910 is considerably smaller than that of the pressure chamber 908, the first stage of the hydraulic pressure is built up.

This hydraulic pressure in the first stage acts on the piston 928, so that the seat 950 is lifted from the ball 948 is, and thus arrives at the delivery chamber 916 and from there to the front brakes 816. When the hydraulic pressure in the ventilation chamber 910 reaches a specified value, in which the force of the spring 986 is overcome, the ball 982 lifts off the seat 984, so that the fluid to the Reservoir 960 can escape. Any further input force applied by the operator now moves the smaller piston section 904 into the delivery chamber 916, so that the second stage of the hydraulic pressure to actuate the wheel brakes begins.

When the input force disappears, the widened piston section 898 detects the plunger 968 so that an undisturbed Fluid communication between the reservoir 960 and the vent chamber 910 is established.

509882/0713

In the embodiment according to FIG. 8, the Pig. 7 corresponding components of the delay device identified by the same reference number.

A tilt valve is located in the compensation opening 956 1062, which is the connection between the vent chamber and the reservoir 960 controls. The tilt valve 1062 includes a valve disc 1064 with a plunger 1066, which is shown in the vent chamber 910 extends and can cooperate with the enlarged piston portion 898 of the piston assembly. A spring 1068 presses the valve disk 1064 against a valve seat 1070. A compensation opening 1052 in the pressure chamber 908 is directly connected to the reservoir 960. This equalization opening 1052 has a considerable amount smaller flow cross-section than the equalization opening 1056.

If the switching valve arrangement 926 is actuated during operation without brake force boosting, in FIG Fluid located in the pressure chamber 908 is conveyed into the venting chamber 910 via the inner chamber 932. There the spring 1068 as a result of the displacement of the enlarged piston section 898 in the bore 902 the valve head 1064 can sit on the seat 1070, the vent chamber 910 is separated from the reservoir 960. If the Has adjusted the piston assembly 894 to such an extent that the

- 39 -

509882/0713

same opening 1052 is located again in the ventilation chamber 910, the hydraulic medium can be used when the switching valve arrangement is opened 926 escape to reservoir 960. However, due to the throttling action of orifice 1052, it becomes faster Prevents fluid from flowing out of chamber 910 and achieves a delay causing the first stage of hydraulic pressure can build up and this hydraulic pressure reaches the delivery chamber 916 and from there to the front wheel brakes 816 .

The delay device thus ensures a delayed switching on of the second operating mode of the servomotor until the first stage of the hydraulic pressure is built up in the enlarged diameter pressure chamber 908, which the brake system supplied with a sufficiently large amount of fluid to be in the smaller diameter pressure chamber 906 to enable the full pressure build-up from an input control force.

509882/071 3

Claims (26)

252639Ί Claims Λ Servomotor with a working section that uses a differential pressure, having working piston controlled by an input force, and a hydraulic delivery section with a Porderkolben arrangement which is slidably arranged in a housing bore and is coupled to the working piston, characterized by a control device actuated as a function of the input force (112, 148, 188), through which the effective piston area of the The delivery piston arrangement (114) and the actuating force generated by the pressure difference at the working section (12) can be reduced transferable to a section (1 28) of reduced effective cross section of the Porderkolben arrangement (114) is. 2. Servomotor according to claim 1, characterized in that the housing bore (126) is formed stepped and with a section (124) of enlarged diameter and one via an outlet opening (196) to a consumer L__J 509882/0713 connectable portion (130) of reduced diameter is provided that the delivery piston assembly (114) a piston surface arranged in the enlarged bore section (124) (122) of larger diameter to delimit a first pressure chamber (126) and one with a hydraulic reservoir (144) connectable ventilation chamber (136) so / ie a piston surface arranged in the narrower bore section (J 30) (128) of smaller diameter to limit a second pressure chamber (146) that in the Conveyor piston arrangement (II4) channels (151, 152, 154) are formed are, through which the first with the second pressure chamber (126, 146) via a first valve (156) and the first pressure chamber (126) with the ventilation chamber (136) Can be connected via a second valve (188) that the second valve (188) by an actuating device (166) depending on the one hand on the input force and on the other hand on an opposing force, from Fluid pressure in the first pressure chamber (126) generated closing force adjustable and adjustable by the closing force is held in the closed position in a first operating mode until the input force exceeds the closing force and in a second operating mode the pressure in the first pressure chamber (126) via the second valve (188) can be reduced, and that by a switching device (148) for the first valve (156) a medium flow - 42 509882/0713 from the second (146) into the first pressure chamber (126) is prevented during the second operating mode. 3. Servomotor according to claim 2, characterized in that the switching device (148) for the first valve (156) coupled to the actuator (166) and the first valve (156) during the first mode of operation in the is kept in the open position, and that the closing 'The first one in succession by virtue of the exceeding input force Valve (156) can be switched into the closed position and the second valve (138) into the open position and the pressure in the first pressure chamber (126) can be reduced. 4. Servomotor according to claim 3, characterized in that the switching device (148) is one in an axial channel (151) of the conveyor cage arrangement (114) arranged sleeve (172) for establishing a flow path from the first (126) to the second (146) pressure chamber in the first Has operating mode, and that the sleeve is provided with a first and a second slot (180, 182) and a pin (162) extending through the two slots on the smaller diameter portion (128) of the delivery piston assembly (114) is attached and the sleeve (172) and the delivery piston assembly (114) when switching to the second operating mode are movable relative to each other. - 43 509882/0713 5. Servomotor according to claim 4, characterized in that that the first valve (156) is arranged in an axial channel (151) Valve plate (158) with a tappet (160) which has a slot through which the pin (162) passes, and a first spring device (I64) includes which the valve plate (158) is pressed in the first operating mode in contact with the pin (162) and one an undisturbed fluid connection from the first pressure chamber (126) to the second pressure chamber (146) can be established is, and that the sleeve (172) by the actuator (166) for the purpose of breaking the fluid communication Can be applied to the valve disk (158) via the first valve (156) and switching to the second operating mode is. 6. Servomotor according to claim 5, characterized in that the second valve (188) is located in an axial channel (151) and a second valve disk arranged on a supporting part (168) belonging to the actuating device (166) (190) and a second spring device (194) fastened to the sleeve (172), through which the second valve disk (190) in the first operating mode to a duct connected to the venting chamber (136) Valve seat (192) is pressed on, and that with an adjustment effected by the actuating device (166) - 44 509882/0713 of the sleeve (172) for the purpose of switching to the second operating mode, the tappets (160) of the first valve disk one after the other (158) can be lifted off the pin (162) against the force of the first spring device (164) and the second The valve plate (190) can be moved away from the associated valve seat (192) against the force of the second spring device (194) is. 7. Servomotor according to claim 6, characterized by one between the support part (168) and one of the input force transferring thrust piston (66, 100) arranged counter-pressure device (170) for generating the operator mediated counterforce. 8. Servomotor according to claim 3, characterized in that in an axial channel (151) in the delivery piston arrangement (114) a first sleeve (472) for producing a first flow path between the first pressure chamber (434) and the second pressure chamber (446) and spring means (480) are arranged through which the first sleeve (472) pressed against the second valve (482, 490) and the connection between the first pressure chamber (434) and the vent chamber (436) is interrupted via a second flow path that the actuating device (466) an actuating piston (484) movable in a sealing manner in the first sleeve (472) and one in the axial channel - 45 - 509882/0713 arranged between the actuating piston (484) and a push rod (400) acted upon by the input force Has counter pressure device (470), and that the actuating piston (434) in the first operating mode with a generated by the pressure in the first pressure chamber (434), via the counterpressure device (470) that of the push rod (400) transmitted input force acts counteracting counterforce and the first sleeve (472) with respect to ~ the delivery piston arrangement (114) in the second operating mode corresponding to an insertion movement of the counter-pressure device (470) caused by the push rod (400) is adjustable. 9. Servomotor according to claim 8, characterized in that the first valve (486, 494) has one on the actuating piston (484) arranged valve ball (486), which is used to shut off the first flow path to one on the first sleeve (472) formed valve seat (494) can be applied. 10. Servomotor according to claim 9, characterized in that the second valve (482, 490) one in the axial channel (151) second sleeve (482) and one in the axial channel between the first and second sleeve - 46 509882/0713 (472, 482) arranged valve plate (490), through which in the first operating mode an ingress of Pressure medium is prevented from the first pressure chamber (434) in the second flow path. 11. Servomotor according to one of claims 2 to 10, characterized by an arranged in the housing to the enlarged portion (124) of the stepped bore (126) ~ connected process (212) to intercept from the stepped bore in the direction of the working piston (28) escaping hydraulic fluid. 12. Servomotor according to claim 3, characterized in that the actuating device (366) has one with an input thrust piston has connected plunger (362) extending into the axial channel (351) of the delivery piston arrangement, by which the first (356) and second (388) valve can be actuated one after the other and the one generated by the working piston (28) Actuating force from the larger diameter piston surface (122) to the smaller diameter piston surface (128) when the input force rises above that when the conveyor cage assembly is pushed into the stepped bore (126) generated by the fluid pressure, opposite acting closing force can be transmitted. - 47 - 509882/0713 13. Servomotor according to claim 12, characterized in that that da3 first valve (356) a valve slide (350) arranged in the axial channel (351) with a seal (358) for isolating a first radial channel (352) leading to the first pressure chamber (334) from a second, to the ventilation chamber (336) leading radial channel, and that connected to the plunger (362) Valve slide (350) the fluid flow from the first pressure chamber (334) via the axial channel (351) in Can be controlled as a function of the adjustment of the plunger (362) determined by the input force. 14. Servomotor according to claim 13, characterized in that the second valve (388) has one next to the second radial channel in the axial channel (351) arranged valve plate (390) to prevent a flow of fluid from the Axially in the second radial channel as well as one between the valve disk (350) and the valve disk (390) effective Has spring device which attaches the valve plate (390) to a valve seat formed in the delivery piston arrangement (392) is pressed. - 48 - 509882/0713 15. Servomotor according to claim 2, characterized in that the larger diameter basket surface of the piston assembly from a sliding on one with the working piston (628) coupled and the center piston (7H) forming the smaller diameter basket surface (128) The annular piston (732) can be moved to a limited extent between two stops (730, 736) attached to the central piston is and resilient inwards into the first pressure chamber "(738) is pressed against the first stop (730), and that the middle piston (7H) with a das first and second valve (750, 768) containing axial channel (722) is provided. 16. Servomotor according to claim 15, characterized in that the switching device of the first valve (750) has a on the annular piston (732) and through slots (764) in the middle piston (7H) extending pin (762) and a first tappet (766) arranged on the pin (762) for actuating the first valve (750) in the event of a displacement of the annular piston (732) in the direction of the first stop (730). 17. Servomotor according to claim 16, characterized in that the first valve (750) is arranged in an axial channel (722) Valve ball and one attached to the middle piston (7H), the valve ball in the direction of a valve seat - 49 - 509882/0713 (754) and the first plunger (766) acting on the spring device (756), the first plunger (766) when the annular piston (732) rests against the first stop (730) holds the valve ball against the force of the spring device (756) in the lifted position from the valve seat (754), and that the valve ball in the first mode of operation by the fluid pressure in the first pressure chamber (738) against the force of the spring device (756) from the valve - Seat (754) can be lifted off and by the spring device in the second operating mode for the purpose of interrupting the fluid connection between the first and second pressure chambers (738, 758) in contact with the valve seat (754) is held. 18. Servomotor according to one of claims 15 to 17, characterized in that that the second valve contains: a valve disk (770) arranged in the axial channel (722), a second, connected to the central piston (714), the valve disk (770) to a surrounding the axial channel The valve seat (772) pressing spring device (774) and a second, connected to the valve plate (770), by the actuating device (666) adjustable tappet (775), by which the valve disc in the second operating mode (770) can be lifted off the associated valve seat (772) and a connection between the first pressure chamber (738) and the venting chamber (740) is producible. - 50 509882/0713 19. Servomotor according to claim 18, characterized in that that the actuating device (666) has an axial bore (786) running through the central piston (714) arranged actuating piston (784). 20. Servomotor according to claim 19, characterized in that that the actuating device (666) one in the axial bore (786) between the actuating piston (784) and the central piston (714) arranged buffer (794) to prevent the actuating piston (784) effected adjustment of the second plunger (775) before the end of the first operating mode. 21. Servomotor according to one of claims 2 to 20, characterized by a delay device 062) through which at the beginning of the second operating mode, a fluid flow from the ^ first pressure chamber $ 08) to the hydraulic accumulator (960) is delayed. 22. Servomotor according to claim 21, characterized in that the delay device is connected to the delivery piston arrangement (896) has coupled tilt valve (962) which, when decoupled from the delivery piston arrangement (896) prevents a flow of fluid from the venting chamber (910) into the hydraulic accumulator (960). - 51 - 509882/0713 23. Servomotor according to claim 22, characterized in that in the housing between the first pressure chamber (908) and the Hydraulic accumulator (960) has a first opening (952) which "when the delivery piston arrangement (896) interacts with the Tilt valve (962) provides an unobstructed fluid connection between the first pressure chamber and the hydraulic accumulator releases, and between the ventilation chamber (910) and the hydraulic accumulator (960) a second opening (956) 'is formed, in which the tilt valve (962) is arranged is, wherein the first opening (952) has a much smaller flow cross-section than the second opening (956) has, and that during an insertion movement of the delivery piston assembly into the housing bore (900) on the first Opening (952) past the first pressure chamber (908) separated from the hydraulic accumulator (960) in the first operating mode and with a further pushing movement of the delivery piston arrangement into the housing bore (900), the venting chamber (91 θ) is connectable to the first opening (952). 24. Servomotor according to claim 22 or 23, characterized in that the tilt valve (962; 1062) da3 has a valve plate (964; 1064), which in one the ventilation chamber (910) with the. Hydraulic accumulator (960) connecting duct (956, 958; 1056) arranged in the housing and with one extending into the venting chamber (910) in contact with the delivery piston arrangement (896) Valve tappet (968; 1066) is connected, as well - 52 - 509882/0713 a valve spring (970; 1068) which encloses the valve plate at one of the channel (956, 958; 1056) in the housing Valve seat (974; 1070) presses on. 25. Servomotor according to claim 24, characterized in that the tilt valve (962) has one between the valve plate (964) and the valve stem (968) located, cylindrical valve body (966) and the valve plate (964) is penetrated by an axial bore (978) running in the valve body (966), which via a bore in the valve body (966) formed Hadialkanal (980) with the between the valve seat (974) and the ventilation chamber / 1st, (910) running flow path ⁷ and that in the channel a valve ball (982) pressed by a spring device (986) on the valve plate (964) of the tilt valve (962) is provided, which is in the on the valve plate (964) seated position prevents a fluid connection via the axial bore (978) when the valve tappet (968) is actuated by the delivery piston arrangement (896) and this fluid connection via the axial bore (978) is prevented when the fluid pressure in the venting chamber (910) exceeds the force of the spring device (986). releases. 26. Servomotor according to one of the preceding claims, characterized in that the actuating device (166) 509882/0713 with a control rod operated by the operator (60) coupled and duroh an adjustment of the control rod at the same time one the pressure difference on the working piston (28) controlling valve arrangement (58) can be actuated. B09882 / 0713