DE102004029883A1 - Servo steering unit for private motor vehicle has valve arrangement with 3/2 directional valves allocated to each working chamber of cylinder and designed as sliding spools with open center position - Google Patents

Abstract

The servo steering unit (100) for a vehicle has a valve arrangement (23) to control a piston (4a) dividing a working cylinder (4) into two working chambers (4b,4c). The valve arrangement has 3/2 directional valves (6,36) allocated to each working chamber and designed as sliding spools with an open center position. The 3/2 valves are each connected to a hydraulic supply (200) via pressure line (10) connected to a line connection, and via a return line (42) connected to another line connection, and also connected to the working cylinder via connecting line (5,37) connected to a line connection. An independent claim is included for a method for the operating of the proposed servo steering system.

Description

The The invention relates to a power steering apparatus according to the preamble of the claim 1 specified type.

A Power steering device of this type is in road vehicles, preferably introduced in passenger car construction. The known power steering device, also called power steering, has a combination of a pump set with a double-acting Working cylinder, both with the interposition of valve assemblies interact in a predetermined way. The control can by a driver-operated steering device respectively. This is directly mechanically connected to the same positively coupled steerable vehicle wheels.

Hydraulic assisted power steering systems of simple design, however, are prone to pressure surges that operate on the steering system. That is why in EP 427 029 B1 has been proposed to connect the pump with a pressure accumulator. Furthermore, elements for damping pressure surges should be installed in the connecting lines from the control valves to the working cylinder. The additional pressure accumulator and the damper elements are expensive components.

The damper elements and speak the pressure accumulator in the supply lines of the working cylinder also with repercussions from the power cylinder and make the steering spongy and lead to a loss of the familiar steering feel.

After EP 999 971 B1 should also be combined with the pump pressure accumulator, while the control is carried out by combined 3/3-way valves, which also have the function of an adjustable pressure relief valve. The proposed 3/3-way valves have a central position in which all connections of the system are separated. The center position is used exclusively to obtain a blocking position, which makes a manual steering impossible. in case of failure of the control unit, the supply lines to the working cylinder to be depressurized and connected to the fluid container.

Other known steering devices are to ensure the functionality executed with a pump set, in which a pressure relief valve is integrated. Disadvantageous is that at maximum steering impact no fluid flow through Valve and cooling assemblies flows and therefore the entire volume flow of the pump via the pressure relief valve stream got to. This causes thermal problems.

A known under the name Servotronic steering embodiment a power steering device used for the actual control of the double-acting cylinder a valve with rotary valve. Such rotary valves must made to ensure the function with extraordinary precision become. The same applies the rotary valve arrangement and contained therein pockets or connecting holes. To ensure necessary adjustments it is necessary to make further dimensional and geometrical adjustments which, even with the application of the latest technologies, is costly and are not always successful. The proposed rotary valves always switch in direct dependence from the geometry of the valve and always both ports at the same time. A disadvantage of this type of rotary valve valve design, that only then a power steering assistance takes place when actually one Deflection of the steering device takes place. Influence on the support behavior independently From the deflection of the steering device are not possible in this respect. One Another problem is the labeling of the corresponding Items and their reliable Combination to the finished rotary valve or its assignment to a specific vehicle type. Likewise, the stockpiling for replacement needs in the multiplicity embodiments be problematic.

Of the The invention is therefore based on the object, the previously used Rotary valve by cheaper and the required performance better, but at least equivalent, fulfilling To replace assemblies while maintaining the usual steering feel. A Another object of the invention is that lying in the side stream Volume flow control valve dispensable.

These Task is for the power steering apparatus by the characterizing features of Claim 1 solved in conjunction with its generic features.

The under claims form advantageous developments of the invention.

Of the Invention is based on the finding that the rotary valves used are enormously complex in terms of production technology and costs, the use of simple manufacturable valve assemblies and the resolution of the main control valve in individual blocks in conjunction with a changed Design of the system and the control unit itself considerable advantages brings.

in the special was found that a balanced steering behavior by the mechanical decoupling of the two directional valves and their exclusive control with electrical signals the possibility offers, using the inventively proposed valve assemblies the Adjust steering behavior so that the behavior of the proposed System can be adapted to different vehicles as well, as in certain driving situations.

To The invention provides a pumped by a pump fluid flow through a Pressure line to the connections fed to two 3/2-way valves. The Constant maintenance of the volume flow takes place in a known manner by a downstream of the pump, known as a flow control valve, Volume flow control valve. The two 3/2-way valves are in turn on the Valve outlet connected to a working cylinder.

In Advantageously, this can be a linear acting cylinder be with double-sided piston rod. Connect in their basic position the 3/2-way valves connect the working cylinder to the return line, so that no fluid pressure can arise in the working cylinder. This also applies if the pump delivers a volume flow. In this switching state, which is approximately a vehicle with a stationary engine or except When the pump is set, the power steering is also out of order. Steering is at significantly increased operating forces anyway possible.

in the general operating condition of a moving vehicle and at a promote a fluid flow Pump are the 3/2-way valves by control signals in the middle position been moved. There they are kept floating. In this switching position is the longitudinal slide just deflected so that an equal opening cross-section between Pump connection and the respective connection of the working cylinder and between the same and the return port. Both 3/2-way valves in the described switching position held, the pumped by the pump fluid flow is divided into the same Share between the two 3/2-way valves. This special switch position the two 3/2-way valves leads to a balanced pressure ratio in the two chambers of the working cylinder.

are Steering movements are necessary on a steering device, both become the 3/2-way valves deflected from the middle position. Corresponding the direction of the steering movement is one of the two 3/2-way valves deflected in the way that the opening cross-section between pump connection and connection to the respective chamber of the working cylinder reduced and to the same extent the opening cross section of the respective another 3/2-way valve between pump connection and connection of the opposite chamber of the working cylinder is enlarged. By this switching position, the pressure balance is disturbed and the piston the working cylinder starts to move.

The Both 3/2-way valves are electrically, preferably via electromagnetic actuations deflected. The control signals are supplied by a control unit, derives these from sensor signals from the steering device come. In this case, the control signals according to predetermined algorithms with the help of electrical or electronic switching elements, but preferably by existing in the control unit computer and generated by the program products stored there for their operation.

The 3/2-way valves are designed as valves with longitudinal slide and can both as individual devices as well as in a version for the bore installation (cartridge) are used. You own due their design adjustment options Requirements resulting from plant design and operation. Since they are controlled by signals from a control unit, they can advantageously optimized in complex with the control unit become.

A preferred embodiment used for the 3/2-way valves the execution for bore installation and a two-chain link.

In a further embodiment, a pressure limiting valve and a 2/2-way valve are integrated into the interlinking block. In this embodiment, it follows that the fluid flow has to traverse a larger line length to the pressure relief valve. If this results in an inadmissibly high pressure for the execution of operations, this is derived via the pressure relief valve in the return line and cooled back in any case via the existing oil cooler. As a result, inadmissible heating of the fluid can be avoided. It is an optimization task to bring the switching behavior with the requirements of the operation of the vehicle in accordance. The additionally arranged 2/2-way valve is provided as an emergency valve in the event that the two 3/2-way valves have impermissible switching combinations, have mechanical damage or were incorrectly controlled by malfunctioning of other components. The 2/2-way valve is a design with spring return, so that the blocking position of this valve can only be achieved by applying a voltage, a signal. The operated in blocking position 2/2-way valve is at Occurs switched a fault and establishes a line connection between the pressure and return line. In this case, an emergency steering can be achieved by applying increased steering forces to the steering device. If, for example, the voltage on the vehicle fails, this valve immediately returns to the normal position through the spring return and switches off the connection between the pressure and return line.

The Steering device is equipped with at least one sensor, the to the control unit signals via the intensity the steering movement delivers. Preferably, the steering device with a torque and in addition equipped with a rotation angle sensor. The signals of both sensors allow It allows the control unit to detect the steering movement after deflection and intensity and tune the behavior of the power steering accordingly.

A another embodiment the invention provides, the 3/2-way valves equipped with a shift position sensor, the switching position of the longitudinal slide detected. Likewise, in the supply line to the working cylinder ever one Pressure sensor to be integrated, resulting from the switching operations Pressure build-up or dismantling determined. Thus, the control unit can operating conditions detect the power steering and even with smaller deviations in the operating behavior appropriate adjustments of the operating regime make. Ultimately, it is optimization task for the controller and in it stored program products.

Further Advantages, features and applications of the present Invention will become apparent from the following description in conjunction with the embodiments shown in the drawing.

The Invention will be described below with reference to the drawings embodiments described in more detail. In the description, in the claims, the abstract and in In the drawing, the list given in the back of the reference numerals used terms and associated reference numerals. In the drawing means:

1 a schematic representation of the power steering used;

2 the representation of the opened in the direction of the return port longitudinal slide and the associated operating points in the diagram;

3 the representation of the center division of the longitudinal slide used and the associated operating points in the diagram, and

4 The illustration in the direction of the pump connection open longitudinal slide of the used 3/2-way valve and the associated operating points in the diagram.

The power steering device according to the invention 100 has a pump 16 on, which is a fluid from the fluid container 17 against a flow control valve 15 promotes, according to the flow control valve 15 existing volume flow corresponds to a desired law. After this hydraulic supply 200 is in the line a stretch hose 14 inserted, which helps to reduce pressure surges.

The pressure line 10 is with a first 3/2-way valve 6 and a second 3/2-way valve 36 connected. Both directional valves 6 and 36 are located inside a valve arrangement 23 , As a result, the cost of connecting cables can be minimized. From the first 3/2-way valve 6 is over the line 5 the cylinder chamber 4b the double-sided working cylinder 4 connected. The second 3/2-way valve 36 is over the line 37 with the cylinder chamber 4c of the double-acting cylinder 4 connected.

Over a coupling rod 3 is the working cylinder 4 with the steering gear only schematically illustrated here 2 connected. Is at the steering device 1 , preferably on the usual steering wheel, generates a rotational movement, this is via the steering gear 2 and the coupling rod 3 directly to the working cylinder 4 transmitted.

The steering device 1 is with a rotation angle sensor 21 and a torque sensor 22 both equipped with their measuring signals to a control unit 20 to transfer. The information obtained about the angle of the steering wheel movement and the intensity of the movement of the steering wheel are by the control unit 20 evaluated and appropriate control signals to the 3/2-way valves 6 and 36 sent out.

The 3/2-way valves 6 and 36 are over 4 connections to the pressure line 10 , the return line 42 and the connection line 5 to the working cylinder 4 - Connection 27 and 53 - Connected, wherein the connecting line in the 3/2-way valve 36 the reference number 37 instead of 5 having. The connection line 5 connects the workspace 4b of the working cylinder 4 with the 3/2-way valve 6 while connecting line 37 the workroom 4c of the working cylinder 4 with the 3/2-way valve 36 combines.

With the 3/2-way valves 6 and 36 these are slide valves with spring return, wherein in the initial state, a connection between the return line 42 and connection line 5 as well as the 3/2-way valve 36 a connection between the return line 42 and connection line 37 consists. In this state is the working cylinder 4 depressurized and it can be steered manually. Through the power steering device 100 there is no power assistance.

Will the power steering device 100 put into operation, sends the control unit 20 first to the 3/2-way valves 6 and 36 Control signals, causing the electromagnetic actuators 7 and 39 Move the longitudinal slide so far that a middle position is taken floating. In this switching position is the longitudinal slide 32 deflected in the way that the opening cross-sections between the pump port 28 and the respective cylinder chamber connection 27 and between cylinder chamber connection 27 and the return port 50 adjust to the same extent. This symmetrical switching position causes that of the pump 16 delivered volume flow in equal proportions between the two 3/2-way valves 6 and 36 split and thus a balanced, low pressure level in the two chambers 4b and 4c of the working cylinder.

Receives the control unit 20 from the angle of rotation 21 and / or torque sensor 22 because of an actuation of the steering device 1 Measuring signals, sends them to the 3/2-way valves 6 and 36 Control signals through which the electromagnetic actuators 7 and 39 the two longitudinal slides 32 deflect out of the middle position. Depending on the type of movement on the steering device 1 be the two 3/2-way valves 6 or 36 controlled as described, resulting in one of the two longitudinal slide 32 in the direction of the return connection 50 opens and to the same extent the respective other longitudinal slide in the direction return port 50 closes. By this switching position, the balanced pressure level in the chambers 4b and 4c of the working cylinder disturbed and the piston 4a starts to move. The intensity of the steering movement determines the amplitude of the deflection of the two longitudinal slide 32 and hence the resulting pressure difference.

The 3/2-way valves 6 and 36 are equipped with measuring and control devices to ensure the functions of the system. At the 3/2-way valve 6 this is a switch position sensor 8th , as well as a pressure sensor 9 who is in the connection line 5 connected. At the 3/2-way valve 36 this is according to the shift position sensor 40 as well as the pressure sensor 41 with connection to the connection line 37 , The through the sensors 8th . 9 . 40 and 41 supplied measuring signals are also from the control unit 20 evaluated and converted into appropriate control signals.

If errors occur in the evaluation of the switch positions, the control unit can 20 either the 3/2-way valves 6 and 36 or if it persists, the 2/2-way valve can continue to operate if a fault condition persists 12 control and make an emergency shutdown. This is a valve, which at the same time an electromagnetically actuated actuator 44 and a spring return 43 has. In the spring return 43 forced switching position, which is also the basic position, consists in the 2/2-way valve 12 a line connection. The resulting short circuit makes the system depressurized, so that no unwanted movements of the working cylinder 4 due to possible faulty switching of the 3/2-way valves 6 and 36 can arise.

Further, between pressure line 10 and return line 42 a pressure relief valve 13 switched on, by which the maximum pressure is limited in its height.

• – In dem in 2 gezeigten Auslenkungszustand ist einer der beiden Längsschieber 32 der beiden 3/2-Wegeventile 6 bzw. 36 derart ausgelenkt, dass der Öffnungsquerschnitt zwischen Pumpenanschluss 28 und Zylinderkammeranschluss 27 auf ein Minimum reduziert und folglich der Öffnungsquerschnitt zwischen dem Zylinderkammeranschluss 27 und Rücklaufanschluss 50 auf ein Maximum erweitert ist. Beim jeweilig anderen 3/2-Wegeventil 6 bzw. 36 wird der Längsschieber 32 gegensätzlich derart ausgelenkt, dass der Öffnungsquerschnitt zwischen Pumpenanschluss 28 und Zylinderkammeranschluss 27 auf ein Maximum erweitert und der Öffnungsquerschnitt zwischen dem Zylinderkammeranschluss 27 und Rücklaufanschluss 50 auf ein Minimum reduziert ist (siehe 4). Stationär betrachtet sind die Summen der Öffnungsquerschnitte pro Wegeventil 6 und 36 allerdings gleich, sodass sich im stationären Betriebszustand der von der Pumpe 16 kommende Volumenstrom zu gleichen Anteilen zwischen den beiden 3/2-Wegeventilen 6 und 36 aufteilt. Da die einzelnen Öffnungsquerschnitte allerdings maximal asymmetrisch sind, wird sich auch ein maximaler Druckniveauunterschied zwischen den Zylinderkammern 4b und 4c einstellen.
• – In der in 3 sichtbaren schwebenden Mittelstellung ist der Längsschieber 32 in der Art ausgelenkt, dass sich die Öffnungsquerschnitte zwischen dem Pumpenanschluß 28 und dem jeweiligen Zylinderkammeranschluß 27 und zwischen Zylinderkammeranschluß 27 und dem Rücklaufanschluß 50 in gleich großem Ausmaß einstellen. Da die einzelnen Öffnungsquerschnitte symmetrisch sind, ist der Druckniveauunterschied zwischen den einzelnen Zylinderkammern 4b und 4c zu Null.
• – In dem in 4 gezeigten Auslenkungszustand ist einer der beiden Längsschieber 32 der beiden 3/2-Wegeventile 6 bzw. 36 derart ausgelenkt, dass der Öffnungsquerschnitt zwischen Pumpenanschluss 28 und Zylinderkammeranschluss 27 auf ein Minimum reduziert und folglich der Öffnungsquerschnitt zwischen dem Zylinderkammeranschluss 27 und Rücklaufanschluss 50 auf ein Maximum erweitert ist. Beim jeweilig anderen 3/2-Wegeventil 6 bzw. 36 wird der Längsschieber 32 gegensätzlich derart ausgelenkt, dass der Öffnungsquerschnitt zwischen Pumpenanschluss 28 und Zylinderkammeranschluss 27 auf ein Maximum erweitert und der Öffnungsquerschnitt zwischen dem Zylinderkammeranschluss 27 und Rücklaufanschluss 50 auf ein Minimum reduziert ist. Stationär betrachtet sind die Summen der Öffnungsquerschnitte pro Wegeventil 6 und 36 allerdings gleich, sodass sich im stationären Betriebszustand der von der Pumpe 16 kommende Volumenstrom zu gleichen Anteilen zwischen den beiden 3/2-Wegeventilen 6 und 36 aufteilt. Da die einzelnen Öffnungsquerschnitte allerdings maximal asymmetrisch sind, wird sich auch ein maximaler Druckniveauunterschied zwischen den Zylinderkammern 4b und 4c einstellen.

The power steering according to the invention can by appropriate deflection of the 3/2-way valves 6 and 36 occupy any operating point. In the following essential 3 characteristic operating points are described:

• - In the in 2 shown deflection state is one of the two longitudinal slide 32 the two 3/2-way valves 6 respectively. 36 so deflected that the opening cross-section between the pump port 28 and cylinder chamber connection 27 reduced to a minimum and thus the opening cross section between the cylinder chamber connection 27 and return port 50 is extended to a maximum. At the respective other 3/2-way valve 6 respectively. 36 becomes the longitudinal slide 32 oppositely deflected such that the opening cross section between the pump connection 28 and cylinder chamber connection 27 extended to a maximum and the opening cross-section between the cylinder chamber connection 27 and return port 50 is reduced to a minimum (see 4 ). Stationary considered are the sums of the opening cross-sections per way valve 6 and 36 however, the same, so that in steady-state operation of the pump 16 coming volume flow in equal proportions between the two 3/2-way valves 6 and 36 divides. However, since the individual opening cross-sections are maximally asymmetrical, a maximum pressure level difference between the cylinder chambers also becomes 4b and 4c to adjust.
• - In the in 3 visible floating center position is the longitudinal slide 32 deflected in the way that the opening cross-sections between the pump port 28 and the respective cylinder chamber connection 27 and between cylinder chamber connection 27 and the return port 50 adjust to the same extent. Since the individual opening cross-sections are symmetrical, the pressure level difference between the individual cylinder chambers 4b and 4c to zero.
• - In the in 4 shown deflection state is one of the two longitudinal slide 32 the two 3/2-way valves 6 respectively. 36 so deflected that the opening cross-section between the pump port 28 and cylinder chamber connection 27 reduced to a minimum and thus the opening cross section between the cylinder chamber connection 27 and return port 50 is extended to a maximum. At the respective other 3/2-way valve 6 respectively. 36 becomes the longitudinal slide 32 oppositely deflected such that the opening cross section between the pump connection 28 and cylinder chamber connection 27 extended to a maximum and the opening cross-section between the cylinder chamber connection 27 and return port 50 is reduced to a minimum. Stationary considered are the sums of the opening cross-sections per way valve 6 and 36 however, the same, so that in steady-state operation of the pump 16 coming volume flow in equal proportions between the two 3/2-way valves 6 and 36 divides. However, since the individual opening cross-sections are maximally asymmetrical, a maximum pressure level difference between the cylinder chambers also becomes 4b and 4c to adjust.

The control unit 20 the power steering system according to the invention is designed so that it from within the power steering device 100 determined measurement signals generated in the respective operating state control signals and to the respective actuators 7 . 39 or 44 sending out. This is done by including in the control unit 20 existing hardware, preferably existing computer modules, as well as additionally stored there program products, with the help of which the hardware works according to programmed algorithms. The control unit 20 can have a specific hardware equipment or consist of a control computer, which in turn controls additional existing power levels, which have the power parameters necessary for the control signals. It is also possible to design the control device so that it also receives outside the existing measurement or control signals, evaluates and generates control signals.

The preferably used 3/2-way valves 6 . 36 are again preferably designed as a bore-hole valves (Cartrige) and consist essentially of a built-in housing 46 , a longitudinal slide in it 32 as well as an electromagnet 26 , At the upper end 47 of the longitudinal slide 32 is a magnetic core 48 arranged in cooperation with the electromagnet 26 the adjustment of the longitudinal slide 32 causes. The hole 27 forms the connection for the working cylinder 4 while drilling 28 the connection for the pressure line 10 forms. The hole 49 of the housing 46 valve assembly 46 takes the longitudinal slide 32 and forms a connection with the coaxial bore 50 in the longitudinal slide 32 the connection for the return line 49 out.

The holes 49 and 50 are over a cross hole 51 connected with each other.

As soon as the control signal for controlling the 3/2-way valve 6 . 36 is missing, it is by the spring 29 moved back to normal position. It is about the connection 53 the chamber 45 with fluid from the working cylinder 4 over the connecting lines 5 . 37 filled and so accelerates the reset process.

The Invention is based on the general idea that the known Transfer technology of today's rotary valves to electromagnetically operated longitudinal slide valves has been. This was the, mechanically operated rotary valve as the 4/3-way valve with open center is executed, by two separate, Electromagnetically actuated, 3/2-way valves also replaced with an open middle. Just like today's rotary valves a permanent volume flow is allowed via the control edges of the 3/2-way valves. this leads to a steering feel which corresponds to today's known power steering systems.

The Invention is characterized in particular by the fact that independent of the deflection of the power steering device a support effect can be applied to the working cylinder. Furthermore, the 3/2-way valves according to the invention are essential simpler and cheaper to produce than today known rotary valves.

One Another major advantage is that the separated Arrangement of the valves the hydraulic support on each side of the working cylinder independently can be adjusted from each other. This can reduce the stiffness of the System can be varied as desired.

One particular advantage of the invention is additionally that in or on the mechanical drive or in or on the forced connection between Steering handle and the vehicle wheels steered therewith no hydraulic control organs must be arranged frictional sealing rings. Accordingly, will in the invention, a steering system with low hysteresis in steering maneuvers with ensures successive changes of direction.

100

Power steering device

200

hydraulic supply

1

steering device

2

steering gear

3

coupling rod

4

working cylinder

4a

piston

4b

Workroom - left

4c

Workroom - right

5

connecting line

6

3/2-way valve

7

actuator

8th

Shift position sensor

9

Pressure Sensor

10

pressure line

11

Return spring

12

2/2 way valve

13

Pressure relief valve

14

Stretch Hood

15

Volume flow control valve, variable

16

pump

17

fluid container

18

filter

19

oil cooler

20

control unit

21

Rotation angle sensor

22

Torque sensor

23

valve assembly

24

piston segment

25

outer casing

26

electromagnet

27

line connection

28

line connection

29

compression spring

30

connection bore

31

coaxial drilling

32

longitudinal slide

33

permanent magnet

34

Pressure pipe connection

35

manifold

36

3/2-way valve

37

connecting line

38

Return spring

39

actuator

40

Shift position sensor

41

Pressure Sensor

42

Return line

43

Return spring

44

actuator

45

chamber

46

installation housing

47

upper end of the longitudinal slide 32

48

magnetic core

49

connection

50

drilling

51

cross hole

52

piston segment

53

line connection

Claims (20)

Power steering device ( 100 ) for a vehicle, in particular for a vehicle with steered wheels, with a pump ( 16 ) having hydraulic supply ( 200 ), one with the steering device ( 1 ) cooperating working cylinder ( 4 ), a valve assembly ( 23 ) for controlling a working cylinder ( 4 ) into a first workroom ( 4b ) and a second workspace ( 4c ) dividing pistons ( 4a ) within the working cylinder ( 4 ) and a control signals in dependence of the movement of the steering device ( 1 ) to the valve assembly ( 23 ) and signals of the steering movement and the states of the valve assembly ( 23 ) detecting sensors ( 21 . 22 . 8th . 9 . 40 . 41 ) receiving control device ( 20 ), characterized in that the valve arrangement ( 23 ) assigned to each working space 3/2-way valves ( 6 . 36 ), which are designed as longitudinal slide with open center position, wherein the 3/2-way valves ( 6 . 36 ) each with the hydraulic supply ( 200 ) via a to a line connection ( 28 ) connected pressure line ( 10 ) and via a to a line connection ( 49 ) connected return line ( 42 ) as well as with the working cylinder ( 4 ) via a to a line connection ( 27 and 53 ) connected connection line ( 5 . 37 ) are connected. Power steering apparatus according to claim 1, characterized in that the 3/2-way valve ( 6 . 36 ) is provided with a hydraulic fluid pressure feedback, which is a chamber ( 45 ), which via the line connection ( 53 ) via the connecting line ( 5 . 37 ) with the working space to be emptied ( 4b . 4c ) of the working cylinder is connected, in which the existing pressure level in the chamber ( 45 ) is constructed. Power steering apparatus according to claim 1 or 2, characterized in that the to the valve assembly ( 23 ) connected hydraulic supply ( 200 ) a flow control valve ( 15 ) having. Power steering apparatus according to one of the preceding claims, characterized in that a first connecting line ( 5 ) the first workspace ( 4b ) of the working cylinder ( 4 ) with the first 3/2-way valve ( 6 ) of the valve assembly ( 23 ) and a second connection line ( 37 ) the second workspace ( 4c ) of the working cylinder ( 4 ) with the second 3/2-way valve ( 3 . 6 ) connects. Power steering apparatus according to one of the preceding claims, characterized in that the 3/2-way valve ( 6 . 36 ) by electrical signals of the signaling device ( 20 ) and an electromagnetically operated actuator ( 32 ) having. Power steering device according to one of the preceding claims, characterized in that the 3/2-way valve as an actuator a longitudinal slide ( 32 ) with one in the chamber ( 45 ) arranged compression spring ( 29 ) cooperates and is arbitrarily movable between a starting position and an end position. Power steering apparatus according to claim 6, characterized in that when the 3/2-way valve is de-energized ( 6 . 36 ) the longitudinal slide ( 32 ) by the compression spring ( 29 ) is held in the initial position of a position in which the pressure line ( 10 ) and the connecting lines ( 5 . 37 ) with the return line ( 42 ) are connected. Power steering apparatus according to claim 6 or 7, characterized in that in the middle position of the longitudinal slide ( 32 ) the connection line ( 5 . 37 ), the pressure line ( 10 ) and the return line ( 42 ) in the manner that the opening cross-sections of all control edges are opened to the same extent. Power steering device according to one of claims 6 to 8, characterized in that the longitudinal slide ( 32 ) in the end position the pressure line ( 10 ) with the connecting line ( 5 . 37 ) and the return line ( 42 ) is interrupted. Power steering apparatus according to one of the preceding claims, characterized in that each of the 3/2-way valves ( 6 . 36 ) independent of the other 3/2-way valve ( 36 respectively. 6 ) by signals from a control unit ( 20 ) according to predetermined algorithms, preferably taking place there stored program products, taking into account sensor signals between a starting position and an end position arbitrary switching positions can take. Power steering device according to one of the preceding claims, characterized in that the 3/2-way valves ( 6 . 36 ) are at standstill of the vehicle in a de-energized state. Power steering apparatus according to one of the preceding claims, characterized in that both of the 3/2-way valves ( 6 . 36 ) upon application of a signal of the steering device ( 1 ) are deflected from the center position in the opposite direction to the same extent. Power steering apparatus according to one of the preceding claims, characterized in that the 3/2-way valves ( 6 . 36 ) Bore hole valves are executed. Power steering apparatus according to one of the preceding claims, characterized in that the valve arrangement ( 23 ) additionally a pressure relief valve ( 13 ) having. Power steering apparatus according to one of claims 5 or 6, characterized in that the valve block ( 23 ) additionally a 2/2-way valve ( 12 ), wherein the same a connection between pressure line ( 10 ) and return line ( 42 ), which is interrupted in the operating state and when a signal of the control unit ( 20 ) establishes a connection. Power steering device according to one of the preceding claims, characterized in that the steering device ( 1 ) a rotation angle sensor ( 21 ) and / or a torque sensor ( 22 ) having. Power steering device according to one of the preceding claims, characterized in that the switching position of the first 3/2-way valve ( 6 ) by a shift position sensor ( 8th ) and the switching position of the second 3/2-way valve ( 36 ) by a shift position sensor ( 40 ) and the measurement results from the control unit ( 20 ) are processed. Power steering apparatus according to one of the preceding claims, characterized in that the connecting line ( 5 ) by a pressure sensor ( 9 ) and the connecting line ( 37 ) by a pressure sensor ( 41 ) and the measuring signals of the pressure sensors ( 9 . 41 ) from the control unit ( 20 ) are processed. Power steering device according to one of the preceding claims, characterized in that the control unit ( 20 ) from the signals of the sensors ( 21 . 22 . 8th . 40 . 9 . 41 ) Information about the operating state of the power steering device ( 100 ) and, if certain, in the control unit ( 20 ) stored operating states, a control signal for the 2/2-way valve ( 12 ) settles and this is thereby switchable from the off in the closed position. Method for operating the power steering device ( 100 ) according to one of the preceding claims, characterized by the following method steps: a. In the absence of fluid flow of the pump ( 16 ) are the 3/2-way valves ( 6 . 36 ) in the starting position and the fluid system is ineffective, with steering movements at increased steering forces on the steering device ( 1 ) possible are; b. In the presence of fluid flow from the pump ( 16 ), the 3/2-way valves ( 6 . 36 ) in the middle position, wherein the fluid flow in the absence of steering movements at the steering device ( 1 ) rotates at low pressure and through Steering movements both of the 3/2-way valves ( 6 . 36 ) are deflected from the center position in the opposite direction to the same extent. The intensity of the steering movement determines the degree of deflection of the two longitudinal slide. c. In the event of a malfunction, the 2/2-way valve ( 12 ) de-energized and by the return spring ( 38 ) is switched to a starting position in which a pressure line ( 10 ) with the return line ( 42 ) is connected, regardless of the switching position of the 3/2-way valves ( 6 . 36 ) a steering movement on the steering device ( 1 ) without support from the fluid system (emergency steering) is possible.