GB2197054A

GB2197054A - Pilot valves

Info

Publication number: GB2197054A
Application number: GB08724571A
Authority: GB
Inventors: Valerian Kremer
Original assignee: Mannesmann Rexroth AG
Current assignee: Bosch Rexroth AG
Priority date: 1986-10-20
Filing date: 1987-10-20
Publication date: 1988-05-11
Anticipated expiration: 2007-10-20
Also published as: DE3635625A1; JPS63115905A; GB8724571D0; GB2197054B

Abstract

A pilot unit comprising: a housing 10, at least one user port (A,B, Figs. 2,3) in said housing, a pump Port P, 34 in said housing, a tank port T, 36 in said housing, spool means (21) arranged in said housing for connecting the pump port and tank port with at least one user port, and an operating element 42(,4) for operating said spool means for selectively providing a fluid communication between said ports, characterized in that at the housing a switching valve 41 is mounted, said switching valve being actuated by said operating element 42. In Figs. 8,9, pivoting of lever 42 about axis 56 from position 49 to position 50 releases a pin 43 and thereby allows spool 80 of switching valve 41 to slide upwardly by a spring 84 to connect its pump port 70 to a signal bore (78,77, Fig. 10) to generate a signal, e.g. to apply a brake. From position 50, pivoting of lever 42 to position 51 or 62 about an axis (3, Fig. 4) actuates one of the spools (21). In another form, Fig. 12, the lever 42 only pivots in one plane from position (53, Fig. 2) to position 51 or 52 and thereby actuates the switching valve 102 hydraulically via the pilot unit 101 and a changeover valve 114. <IMAGE>

Description

SPECIFICATION Pilot Unit The invention relates to a hydraulic pilot unit.

Specifically, the invention relates to a hydraulic pilot unit which operates on the basis of direct operated pressure reducing valves. Such pilot units are used for a pressure-dependent adjustment of valves, pumps, and motors and they are adapted to be installed in a control console. Said pilot units allow an adjustment such that the operator has a close feeling for the adjustment which he is carrying out.

A pilot unit of a known type is shown in the prospectus RD09 305/7.85 of the Mannesmann Rexroth Company in Lohr/Main, West-Germany.

In said known pilot units an operating element is used for operating the pilot unit. The operating element can be moved from its rest position into at least one, preferably however two, operating positions, a first and a second operating position.

Prior to the actuation of the pilot unit into its first or second operating position, it can be desirable to first bring the user (load) which is actuated by the pilot unit, or to bring the apparatus which is actuated by the user into a predetermined operating condition. As an example, it can be desirable when dealing generally with a brake control to specifically provide for a brake venting operation (i.e. the application of a brake) prior to bringing the operating element into its first or second operating position.

It is a general object of the invention to overcome the disadvantages of the prior art and to design a pilot unit such that a hydraulic pressure is generated prior to movement of the operating element into one of its operating positions. The hydraulic signal can then actuate for instance a brake control (and cause the application of a brake).

For a solution of the above-mentioned problem the known control unit is modified by mounting valve means directly to the housing of the pilot unit. Preferably, said valve means are provided in the form of a directional control valve means (switching valve means) and can be mounted by means of flange means directly to the housing of the pilot unit. Said directional control valve or switching valve is realized in the so-called plate or block design, i. e. the valve is connected with the corresponding ports of the pilot unit without the use of tubes or pipes.

Preferred embodiments of the invention may be gathered from the claims.

In accordance with a preferred embodiment of the invention the operating element is a hand-operated lever which operates directly in a mechanical manner the switching valve which is, for instance, used as a venting valve for a brake system.

In accordance with another embodiment of the invention the switching valve (directional control valve) is hydraulically operated if the operating element is actuated. Preferably, the switching valve is hydraulically operated by means of a change-over valve. Said changeover valve is again provided in the so-called platten design, i. e. it does not require any tubes or pipes when mounted to the pilot unit. For this arrangement it is particularly useful to provide means in the form of a spring which will bias a spool into its rest position, with the bias being adjustable so as to allow the adjustment of the switching pressure.

In accordance with another preferred embodiment of the invention a pressure reducing valve is provided in addition to the switching valve. Said pressure reducing valve being mounted at another side wall of the pilot unit and is again of the so-called plate design, i. e.

a design not requiring any tubing.

In accordance with the invention a desirable compact design is achieved. A compact design has advantages with regard to safety.

Additional advantages, objects and details of the invention may be gathered from the description of embodiments shown in the drawing. The drawing shows in Figure 1 a perspective representation of a prior art pilot unit; Figure 2 a sectional view of the pilot unit of Fig. 1 seen along line 2-2 in Fig. 4; Figure 3 a bottom view of the pilot unit of Fig. 2 seen from the direction of arrow 11; Figure 4 a partially cut side-elevational view of the pilot unit of Fig. 2; Figure 5 an enlarged sectional view of Fig.

2; Figure 6 a representation of an application of the pilot unit of Fig. 1; Figure 7 a side-elevational view similar to Fig. 4 but showing a first embodiment of the invention; Figure 8 a detail of the pilot unit of Fig. 7; Figure 9 a representation of the first embodiment of the invention similar to Fig. 7 but showing here essential portions in cross-sectional view; Figure 10 a partially cut view of the pilot unit of Fig. 9 seen from the direction of arrow 39 in Fig. 9; Figure 11 the symbolic circuit arrangement of another embodiment of the pilot unit of the invention used for instance for the control of a brake; Figure 12 the pilot unit of the invention shown in Fig. 11 in a mostly sectional representation; Figure 13 a sectional view along line 13-13 in Fig. 14; Figure 14 the partially cut rear view, i. e. a view from the left in Fig. 12.

At the outset a pilot unit 1 of the prior art will be described with reference to Figs. 1-5.

Thereupon, in connection with Fig. 6, a typical circuit arrangement will be explained in which a pilot unit 1 can be used.

The hydraulically operated pilot unit 1 operates on the basis of direct actuated pressure reducing valves and is shown in the prospectus of the Mannesmann Rexroth company: RD 09 305/7.85.

The pilot unit 1 comprises in essence a housing 2 within which an actuating shaft 3 carrying an actuating element 4 is pivotally mounted.

The pilot unit 1 comprises an upper surface 5, a bottom surface 6, a front surface 7, a rear surface 8 and a left surface 9 as well as a right surface 10. Prior to discussing the design of the pilot unit 1 in detail, a typical application of the pilot unit 1 will be explained by referring to Fig. 6. As shown in Fig. 6 a pump 13 is connected with its input to a tank 14 and is further connected to a user (load) 19. Depending on the position of the actuating element 4 the pump 13 can be connected via the user port A of the pilot unit 1 and the conduit 17 with the user 19 or else, the pump 13 can be connected via the user port B and conduit 18 with the user 19. As is general practice, parallel to the pump 13 a pressure relief valve 16 is provided.The curved arrow shown in Fig. 6 above the operating element 4 indicates the zero or neutral position at 53, a first operating or switching position 51 and a second operating or switching position at 52.

With regard to the design of the pilot unit 1 attention is drawn to Figs. 2-4. The pilot unit 1 comprises in its housing two control spools 21. For reasons of simplicity the following description relates to only one of said control spools 21. Each of the control spools 21 is provided with a control spring 22 and a reset spring 23. Moreover, a pin 24 is provided and in the control spool 21 a spool bore 25 is arranged.

The longitudinal axis of the pilot unit is referred to by the reference numeral 27 in Figs.

1, 3 and 4.

One can recognize specifically in Figs. 2 and 3 that the pilot unit 1 comprises a pump bore 28, a tank bore 29, a first user bore 30 and a second user bore 31 adapted to be connected with appropriate elements. The bores 28-31 extend parallel to the longitudinal axis 27. A pump port 34 extends transversely with respect to the longitudinal axis 27 and connects the first and the second user bores 30, 31 in the area of the spoos 21. A tank port 36 connects the bores 30 and 31, and moreover, a tank port 37 is shown.

The operation of the prior art control unit 1 is known and therefore requires only a short explanation. The operating element 4 is held in its neutral position 53 by the reset spring 23 and oppositely acting spring means not specifically referred to. In case the operating element 4 is actuated, for instance moved towards the operating position 52, then the pin 24 will be moved against the force of the appropriate reset spring 23. At the same time the control spring 22 will move the control spool 21. Therefore, at the beginning of the control movement a connection is provided from the port P via the spool bore 25, and via the port A to the apparatus to be adjusted, i.

e. the user 19. The user 19 can be a valve, a pump or a motor. The adjustment of the user is carried out depending on the position of the operating element 53 and also depending on the characteristic of the control spring.

If one pivots the operating element 4 in the opposite direction towards the first operating position 51, then the other control piston is actuated and a connection is created between the port P via the port B to the user.

The actuating means provided between the operating element 4 and the pins 24 are designed such that only one of the pins 24 is moved while the other pin remains in its shown initial position.

Fig. 7-10 disclose a pilot unit 40 of the invention. This modified pilot unit 40 comprises the prior art pilot unit 1 together with a switching valve (directional control valve, generally valve means) 41 mounted thereto.

The switching valve 41 comprises an actuating element 42 which operates the pilot unit 1 as well as the switching valve 41. The operating element 42 actuates the switching valve 41 by means of coupling or actuating means in the form of a pin 43. Said mechancical actuating means can also be provided in the form of hydraulically operated actuating means.

Fig. 8 discloses in a plan view a guide slot (coulisse guide) 48 provided in guide means 46 which can be designed in the housing of the pilot unit 40. The guide slot 48 is generally in the form of a T and defines the first and second operating position 51 and 52 as well as a first valve switching position 49 and a second valve switching position 50. The second valve switching position 50 corresponds with the zero or neutral postion 53 of the pilot unit 1.

The pilot unit 40 makes it necessary that the operating element 42 is always first moved into the second switching position 50, i.e. the neutral position 53 of the pilot unit 1 prior to an actuation of the pilot unit 1. Due to this necessity prior to an actuation of the pilot unit 1 the switching valve 41 has to be actuated first.

As will be explained below in some detail, due to the actuation of the switching valve 41 a hydraulic signal can be generated which is used to bring a user actuated by the pilot unit 1 into a desired condition. For instance, it can be desirable to apply a brake prior to connecting a user in a hydraulic circuit. This can be done by the hydraulic signal generated by the switching valve 41. Said hydraulic signal will be generated when the operating element 42 is moved from the first switching position 49 to the second- switching position 50.

Fig. 9 discloses a more specific design of the pilot unit 40 of Figs. 7 and 8 with the pilot unit 40 of the invention being shown partially in a sectional view and comprising the pilot unit 1 of the prior art with a directional control valve (switching valve) 41 as well as the operating element 42 mounted thereto.

Bolts 72 and 73 extend through the pilot unit 1 for mounting the switching valve 41 to said pilot unit 1. Also, pin 43 extends through the housing 2 of the pilot unit 1 and is pivotally mounted within said housing 2 by means of bearing means 63 not shown in detail. Pin 43 extends with its one end into a bore 62 provided in a bearing body 55 which is mounted to the operating shaft 3. Bearing body 55 forms the guide means 46 shown schematically in Fig. 8. Fig. 9 discloses the slot 48.

The actuating element 42 is located in an actuating body 57. Actuating body 57 is pivotally mounted in the plane of Fig. 9 between the shown switching position and an operating position. The pivotal movement occurs about a bearing shaft 56 of the bearing body 55. In the positin shown in Fig. 9 the operating element 42 is in the position referred to by reference numeral 49 in Fig. 8. In the shown position the actuating body 57 is in abutment with an abutment surface 58 of the bearing body 55. This is achieved by the force of a spring 60 located in a bore 59 of the bearing body.

The spring 60 applies a force via the actuating body 57 onto the abutment body 61 in a rightward direction. In the position of the operating element 42 shown in Fig. 9 the pin 43 is in its rest position in which it is in abutment with the actuating body 57. Pin 43 can be maintained in this position by means of a spring 84 of the switching valve 41. The spring 84 will be described in some detail below.

Before it is possible that the operating element 42 imparts a pivotal movement onto the operating shaft 3 to move it into the position 52 or the position 51 - in accordance with Fig.

8, it is required that the operating element 42 be pivoted out of the position shown in Fig.

9, with this movement corresponding to a movement from the position 49 to the position 50 in accordance with Fig. 8. For this movement from the position 49 into the position 50 the switching valve 41 is supposed to generate a hydraulic signal which will for instance effect the application of a brake. This hydraulic signal is applied to a signal port bore 77 shown in Fig. 10.

Referring to Figs. 9 and 10 the switching valve 41 will now be described in more detail.

The switching valve 41 comprises a housing 66 into which the bolts 72, 73, already mentioned, are screwed so as to provide mounting at the left side 9 of the pilot unit 1. Inside the housing 66 a bore 68 is provided which extends parallel to the longitudinal axis 27.

Within said bore 68 a spool 80 is reciprocally mounted. Spool 80 is biased into its shown initial position by means of spring 84. Spring 84 is in abutment with one end of the spool and also with a closing screw 85. Spool 80 is in its initial position in engagement with a pin 81. Pin 81 is reciprocally mounted within a plug 82 in bore 68. A seal 83 surrounds pin 81. Pin 81 abuts at a ball 65. The-ball 65 is reciprocally mounted within a recess of the plug 82. The ball 65 in turn is in abutment with a pivotal body 64 which is pivotally mounted in housing 66. The pivotal body 64 abuts on the other hand at an end of pin 43.

A cover 67 closes the top end of the housing 66. By rotating the closing plug 85 the force 84 excerted onto the spool 80 is adjusted in such a manner that spool 80, pin 81, ball -65, pivotal body 64, pin 43 and actuating body 57 contact each other and are in the position shown in Fig. 9. If the actuating element 42 is pivoted leftwardly in Fig. 9 against the force of the spring 60, then the spring 84 can move the spool 80 from the rest position of Fig. 9 upwardly into its operating position.

The housing 66 is provided with two axially spaced bores, a pump port bore 70 and a tank port bore 71. Said bores extend perpendicularly with respect to the longitudinal axis 27 and are arranged at the level of the corresponding pump port bore 34 and tank port bore 36, respectively, in the pilot unit 1.

Bores 70, 71 provide for a connection to the bore 68. Between the two bores 70, 71 a signal port connecting bore 78 is provided and extends in the housing 66 of Fig. 9 rearwardly and in Fig. 10 towards the right. Said bore 78 extends parallel to the left side 9of the pilot unit 1 and perpendicularly with respect to the longitudinal axis 27. The bore 78 is connected with a signal port bore 77 which is shown in Fig. 10 and extends parallel to the longitudinal axis 27. Bore 78 is closed on the righthand side by means of a plug as shown in Fig. 10.

The spool is provided with lands 86, 87 and 88 in such a manner that in the rest position of Figs. 9 and 10 the tank port bore 36 as well as the tank port bore 71 are connected with the signal connecting bore 78, while the pump port bore 74 and the pump port bore 70 are isolated or separated from the signal connecting bore 78. If the spool 80 is moved into the operating position not shown, the pump port bore 70 is connected with the signal port bore 78 and the tank port bore 7 1 is separated from the signal port bore 77. As a consequence, a pressure signal is created in the signal connecting bore 78 and the signal port bore 77, a pressure signal which for instance can be used for actuating a brake directly or indirectly.

The transversal bore referred to by refer ence numeral 76 in Fig. 9 continues inside of the spool 80 in the form of a longitudinal bore and connects the two spaces or chambers which are formed adjacent to both ends of the spool 80. Moreover, Fig. 10 discloses that the cover 66 of the switching valve 41 is mounted to the housing 76 by means of bolts 74.

Based on the above description a man skilled in the art will understand the operation of the pilot unit 40 so that a short summary of the operation will suffice. In Figs. 7 and 9 the operating element 42 for the modified pilot unit 40 is in its neutral or center position with regard to the operation or actuation of the pilot unit 1. This position is shown in Fig.

2 and is referred to by reference numeral 53.

Before it is possible to operate the pilot unit 1 it is automatically required that the operating element 42 is moved leftwardly in Figs. 7 and 9 so that the switching valve 41 is actuated or operated. Thus, the switching valve 41 generates a signal which for instance causes the control of a brake, for instance a brake venting means is actuated so as to cause an application of the brake. Only after the switching valve 41 has been operated the pilot valve 11 can be operated. For instance, the pilot valve 1 can be brought into its first 51 or second 52 connecting position (Fig. 2).

The immediate mounting of the switching valve 41 at the pilot unit 1 leads to a compact design for the modified pilot unit 40, which is moreover of a design providing for a safe operation. Due to the design shown where the switching valve 41 is located at one side 9 of the pilot valve 1 opposite to the side 10 where the operating element 42 is provided, favourable conditions are reached with regard to the hydraulic connecting bore in the switching valve and in the pilot unit with regard to the bores already present in the pilot unit 1.

When the operating element 42 is moved back from the position 50 in Fig. 8 to the position 49 in Fig. 8, the valve spool 8 is again moved back to the position shown in Fig. 9, a movement which is caused by the actuating body 57, the pin 43, the pivotal body 64, the ball 65, and the pin 81.

A modified pilot unit 100 forming a second embodiment of the invention is shown in Figs.

11 to 14. The modified pilot unit 100 comprises in substance see the symbols in Fig.

11-a pilot unit 101 with a switching valve plate (switching valve block, switching valve) 102 mounted thereon, and also in addition a pressure reducing plate (pressure reducing valve, pressure reducing valve block) 103. The pilot unit 101 corresponds substantially to the pilot unit 1 of Fig. 2 as was true with the preceding embodiment; only connecting bores are provided for having a connection to a switching valve. The switching valve 102 of Fig. 11 is no longer mechanically actuated but is hydraulically actuated. For this reason the switching valve plate 102 comprises the proper switching valve 141 as well as hydraulic actuating or operating means 104, and a change-over valve 105.

A pressure reducing valve plate (pressure reducing valve) 103 is provided in accordance with another embodiment of the invention and is designed in the form of a pressure reducing block, which comprises connecting conduits as well as the proper pressure reducing valve 106.

In connection with Figs. 11 through 14 the modified pilot unit 100 and the pressure reducing valve block 103 are described.

Fig. 12 shows that again at the lefthand side 9 of the pilot unit 101 the switching valve 102 is mounted with its housing 66 by means of bolts 72, 73, inserted at the side where the operating element 42 is arranged.

Housing 166 comprises a bore 109 within which a spool 110 is reciprocally mounted.

The bore 109 is closed at the bottom by means of a screw 185 and at the top by a plug 111. In the plug 111 a bore 112 is centrally located and ends in a space formed at one end of the spool 110. A spring 113 maintains the spool 110 in the position shown in Fig. 12 in abutment with the plug 111.

The bore 112 is on the other hand connected with a change-over valve 114 which is shown in detail in Fig. 14. Bolts 116 mount the change-over valve 114 at the housing 166.

The spool 110 comprises lands 117 and 118 which will, depending on the position of the spool, connect a signal connecting bore corresponding to the bore 78 in Fig. 9 with a pump port bore 170 and a tank port bore 171, respectively. The pump port bore 170 is connected with a tank port bore 136 in the pilot unit 101 and the pump port bore 170 is connected with a pump port bore 134 in the pilot unit 101.

The rest position of the spool 110 shown in Fig. 12 a radial bore 119 connects via a longitudinal bore, shown with dotted lines, the tank port bore 136 with the spring chamber 120 provided at one end of the spool 117.

In the rest position of the spool 110 shown in Fig. 12, the pump port bore is blocked and the tank port bore 171 is connected with the signal connection bore 178. This means-see also Fig. 14-that the tank pressure is applied to a connecting bore 177 which extends perpendicularly to the signal connecting bore 178.

If the spool 110 moves into its operating position (not shown), the connection between the tank port bore 171 and the signal port bore 178 is blocked and the signal connecting bore 1 78 is connected with the pump port bore 170.

The movement of the spool 110 from its shown rest position into its operating position is caused by hydraulic means which cooperate with the said change-over valve 114. The change-over valve 114 is designed such that the pilot unit 101 is actuated either due to pressure in a user conduit A or in a user conduit B and applies the appropriate pressure to the spool 110 for its operation.

Inasmuch as the change-over valve 114 is located on top of the switching valve 102, two user port bores 121 and 122 are provided in the housing 166. Said bores 121 and 122 extend parallel to bore 109. The user connecting bore 121 is connected with the port A and the user connecting bore 122 is connected with the user port B. This is shown in Fig. 14. The user connecting bore 122 is connected by means of a connecting bore 123 extending perpendicularly thereto in the housing 166, with a connecting bore 124 in the housing of the pilot unit 101 as is shown in detail. The connecting bore 124 extends to a bore in the housing of the pilot unit 101, a bore which is connected to the user port B. In Fig. 12, said ports A/B are schematically shown by dotted lines.Seals 125 provide a sealing effect at the transitions between the housing 166 of the switching valve 102 and the housing of the pilot unit 101.

Referring now to Figs. 12 and 14, the design of the change-over valve 114 will be described in some detail. Both user connecting bore 121 and 122 are connected by means of bores 126 and 127, respectively, with a longitudinal bore 128 which in turn extends parallel to side 9 of the pilot unit 101. In bore 128 spool 129 is located having at both its ends pins. Spool 129 connects, depending on its position, the user connecting bores 121 and 122, respectively, with a connecting bore 130, a connecting bore 130 which in turn is connected with bore 112. As already mentioned, pressure medium is applied to the pressure chamber 131 formed at the upper end of the spool by means of bore 112.

Fig. 12 shows the rest position of the switching valve 102. The operating element 42 for the pilot unit 101 is in its neutral position. As mentioned, the pilot unit 101 is of the same design as the pilot unit 1 of the prior art, with the exception that ports are provided for the switching valve 102 and the valve 116. This, in the neutral position of the operating element 42, no pressure exists either at the port A or at the port B.How ever, as soon as the operating element 42 is pivoted in the direction towards the switching position 51 or 52 of Fig. 2, a pressure builds up either at the user port A or at the user port B, a pressure which will at once be sup plied via the change-over valve 114 to the pressure chamber 131 of the switching valve 102 and cause a movement of the spool 11 7 against the force of spring 113 such that the pump port bore 170 is connected with the signal connecting bore 178. As a consequence, a pressure is available for controlling purposes at the signal connecting bore 177 as disclosed in Fig. 14. In case that the operating element 42 is again returned to its neutral position, then the spool 117 returns to its shown rest position so that the signal at the signal port bore 177 disappears.

For the embodiment of Figs. 11 through- 14, the operating element 42 needs to be pivotable only in one plane, as is shown for the prior art in Fig. 2.

Specifically in Fig. 12, the pressure reducing block 103, already explained in connection with Fig. 11, is shown. The pressure reducing block 103 comprises a housing 150 which is mounted by means not shown to the lower surface 6 of the pilot unit 101. The housing 150 comprises the actual pressure reducing valve 106. Moreover, in the housing 150, a pump port bore 151 and a tank port bore 152 are provided which are connected by means of connecting bore 153 and 154, respectively, with the bore 164 which is adapted to receive the spool 158 of the pressure reducing valve 106.

The spool 158 is biased into its position shown in Fig. 12 by means of a spring washer 1 59 which is subjected to the force of a spring 160. Spring 160 acts between the spring washer 159 and a plug 161 closing the bore 155.

The operation of the pressure reducing valve is well-known and does not need to be de scribed in any detail. The pressure reducing valve 106 is required inasmuch as typically the pilot unit 101 works with a pressure which is reduced with respect to the pump pressure.

For instance, the pilot unit operates with a pressure of 50 bar. So far, either-an auxiliary pressure source was used or else, a separate pressure reducing valve was required.

The invention provides for a pilot unit 101 in a so-called plate design which allows for the immediate mounting of a pressure reduc ing valve 106. Preferably the pressure reduc ing valve 106 is provided in the form.of a pressure reducing valve block 103 at the lower surface 6 of the pilot unit 101. The bolts required for mounting the pressure re ducing valve block 103 at the housing of the pilot unit 1 are not shown.

All in all the invention provides for an appa ratus of compact design which is desirable for safety reasons.

Claims

1. A pilot unit (40,100) comprising: a housing (10), at least one user port in said housing, a pump port in said housing, a tank port in said housing, spool means arranged in said housing for con necting the pump port and tank port with at least one user port, and an operating element (42) for operating said spool means for selectively providing a fluid communication between said ports, characterized in that at the housing (10) a switching valve (41,141) is mounted, a switching valve which is actuated or switched by means of the operating element (42).

2. Pilot unit of Claim 1, characterized in that said operating element (14) switches said switching valve (41) by mechanical coupling means.

3. The pilot unit of Claim 1, characterized in that said operating element (42) operates said switching valve (141) hydraulically.

4. The pilot unit of Claim 3, characterized in that said switching valve (141) is switched by means of the pressures occurring at the user port (s).

5. The pilot unit of one or more of the preceding Claims, characterized in that within said housing (10) at least two user ports (A, B) or pairs of such user ports, are provided, and that the operating element is pivotally mounted at one side (10) of the pilot unit between a neutral position (53) and a first switching position (51) and a second switching position (52), and that the switching valve (41) is provided at the opposite side (9) of the switching valve and comprises in its housing (166) bores (70, 71) which are connected with bores in the housing (2) of the switching valve, bores which are in turn connected with the pump port (P) and the tank port (T), respectively.

6. Pilot unit of one of the preceding Claims, characterized in that the spools (21) are reciprocally mounted in bores which extend parallel to the longitudinal axis (27) of the pilot unit, while the connecting bores (70,71) extend in the housing (66) of the switching valve (41) and the connecting bores (34,36) extend in said housing (2) of the switching valve (1) perpendicularly to the said longitudinal axis (27).

7. Pilot unit of one or more of the preceding Claims, characterized in that the switching valve (41) comprises a spool (80) in a longitudinal bore (68), the spool is reciprocally moveable between a rest position and an operating position so as to connect the pump port bore (70) and the tank port bore (71), respectively, with a signal connecting bore (78) in said housing (66) so as to supply according to the position of the spool (88) a hydraulic signal, or to not supply such a signal.

8. The pilot unit of one of the preceding Claims, characterized in that said spool is biased into its rest position by spring means (84) and can be moved from its rest position to its operating position by mechanical cou pling means (43, 64, 65, 81) which can be actuated by means of said operating element (42).

9. The pilot unit of one of the preceding Claims, characterized in that the operating element (42) is guided in guide means (46) in such a manner that prior to the actuation of the pilot, the switching valve is actuated.

10. The pilot unit of one of the preceding Claims, characterized in that the switching valve directly mounted to the pilot unit makes it impossible that the signal generation of the switching valve is influenced from the outside at will.

11. Pilot unit of one of the preceding Claims, characterized in that due to the direct mounting of the switching valve to the control unit, a mechanical distortion of the signaltransferring elements is precluded.

12. The pilot unit of Claim 3, characterized in that instead of the switching valve in the connecting plate, pressure switches are provided which will supply electrical signals after an adjustable pressure in the user ports has been reached.