DE3111765A1 - "HYDRAULIC SYSTEM FOR FORKLIFT" - Google Patents

Description

TER MEER · MÜLLER · STEINMEISTER Nissan

DESCRIPTION

The invention relates to a hydraulic system for forklift trucks according to the preamble of the main claim. 5

Forklift trucks have an upright column on which a forked carriage goes up and down is movable.

Different hydraulic circuits have already been proposed for such forklifts. One of those well-known Hydraulic circuits is shown in FIG. 1. From a container 1 for receiving a working fluid, in particular oil, a suction line 2 goes out, at the inlet end of which a filter 3 is located. The suction line 2 opens into a hydraulic pump 5 with constant output, which in turn is connected to an electric motor 4, so that the hydraulic oil out the container 1 is sucked off via the suction line 2 with the aid of the hydraulic pump 5. The outlet of the hydraulic pump 5 is connected to a line 6, which in turn opens into the container 1. There is a tilt valve on line 6 8, which is connected to two tilt cylinders 7, and downstream of the tilt valve 8, a lift valve 10, the is connected to a lifting cylinder 9, which has a larger volume than the tilting cylinder 7. The lift valve 10 is also connected to the line 6 upstream of the tilt valve 8 via a bypass line 11. First and second connecting lines 12 and 13 connect the line 6 to the tilting valve 8 and the lift valve 10. The bypass line 11 and the line 6 are connected downstream of the lift valve 10 by means of a pressure relief valve 14, the serves to deliver the oil from the bypass line 11 into the line 6 downstream of the lift valve 10 when the pressure of the oil in the bypass line 11 and the line 6 upstream of the tilt valve 8 and the lift valve 10 exceeds a predetermined value. When the lift valve 10 is a first

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Assumes switching position I and the lifting cylinder 9 is filled for lifting the carriage provided with a fork, the oil arrives with the aid of the hydraulic pump 5 in the lifting cylinder 9 via the line 6, the bypass line 11 and the lift valve 10. When the fork is loaded beyond a predetermined weight, the pressure relief valve allows it 14, that the oil flows off through the pressure relief valve 14 in the direction of the container 1. If on the other hand the fork is loaded within the permissible weight range, the pressure relief valve 14 remains closed.

When the lift valve 10 and the tilt valve 8 in a second Switching position II or a first switching position III are switched over, the tilting cylinders 7 are acted upon and the column of the forklift is tilted backwards. In this case, the bypass line 11 is through the Lift valve 10 closed, so that the oil from the hydraulic pump 5 to the tilting cylinders 7 via the line 6 and the Tilt valve 8 can get. As a result, the tilt cylinders 7 cause the column of the forklift truck backwards is tilted. The flow of the oil is during the entry into the tilt cylinder 7 through a throttle valve 15 within of the tilt valve 8 is controlled so that the operating speed of the tilt cylinder is kept within a predetermined range will. This has the result that the pressure of the oil in the line upstream of the tilt valve 8 up to the response pressure of the pressure relief valve 14 is increased so that part of the oil from the hydraulic pump 5 is returned to the container 1 will.

Since bi'i a known hydraulic circuit of the described Kind of a part of the oil from the pump 5 in the container 1 via the pressure relief valve 14 is returned, the pressure the oil in line 6 upstream of the tilt valve 8 is increased up to the response pressure of the pressure relief valve 14, So that the electric motor 4 consumes an unnecessary amount of energy

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needs. In addition, disruptive noises arise when the oil passes through the pressure relief valve 14.

The invention is therefore aimed at creating an improved hydraulic circuit of the generic type, in which the energy consumption of the drive motor is reduced and annoying noises that occur when passing through the Oil through a pressure relief valve, be switched off

The invention results in detail from the characterizing part of the main claim.

The hydraulic circuit according to the invention for forklifts includes a container for holding hydraulic oil, a container extending therefrom and connected to a hydraulic pump Suction line, another line emanating from the hydraulic pump, which runs back to the container, and oil returns to the container, at least one tilt cylinder for tilting the column and a lifting cylinder for lifting and lowering the forked carriage.

Appropriate control valves are provided to control the lifting cylinder and the tilting cylinder. The tilt valve has two throttled channels that allow some of the oil downstream of the tilt valve then into the container due when the tilt valve in the tilt cylinder supplies oil. A lift valve is located on the from the hydraulic pump outgoing line downstream of the tilt valve and is used to control the lifting cylinder.

In the following, preferred exemplary embodiments are based on the accompanying drawing explained in more detail.

Fig. 1 is a schematic diagram of a

conventional hydraulic circuit; 35

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Nissan

Fig. 2 is a schematic side view

a forklift truck for which the hydraulic system according to the invention is provided;
5

Fig. 3 is a schematic diagram of a

Embodiment of the invention;

Fig. 4 is a longitudinal section through a tilt valve for the hydraulic system

according to FIG. 3 and shows this in the neutral position;

FIG. 5 is a similar longitudinal section, but shows the tilt valve of FIG. 4 in FIG

the first operating position;

Fig. 6 is a further longitudinal section corresponding to Fig. 4 and shows the tilt valve in a third position;

Fig. 7 is a partial section corresponding to Fig.

Fig. 6 shows a state in which the oil after tilting the column does not get to the tilt valve at the front;

Fig. 8 is a section similar to Figs

illustrates another embodiment of the invention; 30th

Fig. 9 is a longitudinal section accordingly

Fig. 8 and shows a position in which the column in a rearward tilted position is held; 35

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Fig. 10 is a longitudinal section of the tilt valve

8 in a position in which the column is kept tilted forward;
5

11 is a partial section corresponding to FIG.

10 and shows the position in which the oil during the tilting movement of the column forward does not get to the tilt valve.

In the following description, the terms "above" and "below" refer to the corresponding areas of the drawing or individual parts of the drawing. However, it is not necessary that the lift valve or the tilt valve in a corresponding Orientation to be mounted.

The forklift shown in Fig. 2 is designated as a whole by 31 and comprises a chassis 32, a towering one Column 33, the lower end of which is pivotally connected to the chassis 32 so that the column is forward and can be tilted backwards, and a carriage 34 provided with a fork 35 that moves up and down is displaceable on the column 33. Two tilt cylinders 36 are pivotable with the chassis 32 by means of an axle pin 37 connected and have piston rods 38, the front ends of which are also pivotable with the column 33 in Are connected so that the column 33 can be tilted forward when the piston rods 38 of the tilt cylinder 36 can be extended. A lifting cylinder 39 is fixedly attached to the column 33 and has a piston rod 40 on, the front end of which carries a freely rotatable chain wheel 41. A chain 42 runs around the sprocket 41 and is fixed with one end to the lifting cylinder 39 and the other end to the carriage 34, so that the Use the chain to move carriage 34 up and down

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can be moved away when the lifting cylinder 39 is extended or is contracted.

An embodiment of a hydraulic system according to the invention 43 is shown in Fig. 3 and includes a reservoir 44 for supplying the system with oil. A suction line 45 takes oil from the container at one end via a filter 46 and is at the other end with the inlet of a hydraulic pump 47 connected to a fixed output which is driven by an electric motor 48. A line 49 goes from the hydraulic pump 4 7 and is in the further course via a filter 50 and a line 51 with the container 44 connected. On the line 4 9, a tilt valve 52 is provided, which via second and third lines 53 and 54 with front and rear chambers 55,56 is connected, which form the tilt cylinder 36 and serve to the column 33 after to pan forward and backward.

The structure of the tilt valve 52 can be seen in greater detail in FIG. 4. The tilt valve 52 includes a valve housing 57, the is provided with a bore 58 in the axial direction. The housing 57 has annular grooves 59, 60, 61, 62, 63, 64, 65, 66 and 67, which are arranged in this order from the upper to the lower end of the housing 57 coaxially with the bore 58 so that the annular grooves 59 to 67 are connected to the bore 58. The grooves 59 to 67 have a larger diameter than the bore 58. A passage a extends from the outer peripheral surface of the housing 57 from, which is in communication with the grooves 62 and 64. Correspondingly, passages b, c, d, e, f, g and h are included the grooves 59,60,61,63,65,66 and 67 connected. In the bore, a valve body 68 is slidably arranged, the upper end is connected to a lever 6 9, as FIG. 3 shows.

Thus, the valve body 68 can be adjusted with the aid of the lever 69

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can be moved up and down. The movement of the valve body 68 is sensed by a limit switch 70, which is placed with a finger 71 on the upper side of the valve body 68 engages when the tilt valve 52 is in its neutral position as shown in FIG.

According to FIG. 4, webs or rings 72, 73, 74, 75 and 76 are formed on the valve body 68, in this order are arranged from top to bottom. The rings 72,73,74 and 76 have an outer diameter which is in substantially corresponds to the inner diameter of the bore 58, while the ring 75 has a slightly smaller diameter than this owns. The ring 75 has a cutout 77 at its lower end. In the same way is the ring 76 is provided with a cutout or bevel 78 at its upper end. In the lower half of the valve body 78 is a bore 79 which runs in the axial direction of the valve body 68 and a receives further valve body 80, the outer diameter of which is smaller than the inner diameter of the bore 79, The The valve body 80 has rings 81 and 82 on the circumference, the outer diameter of which is essentially the same as the inner diameter corresponds to the bore 79. The outer surface of the ring 75 communicates with the bore 79 via a channel 83, and the outer surface of the valve body 68 between the lands 75 and 76 is with the bore 79 via a channel 84 connected. Furthermore, the outer surface of the ring 76 is connected to the bore 79 via a channel 85. A screw 86 is screwed into the lower end of the valve body 68 and closes the bore 79, and a compression coil spring 87 is located between the lower end of the valve body 80 and the screw 86 so that the Valve body 80 is biased upward.

A spring housing 88 forms a cavity 89 which extends in the axial direction of the housing 57 and at the upper end

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of the spring housing 88 is open. The spring housing 88 is fastened to the lower end of the housing 57 in such a way that the cavity 89 meets the bore 58 so that the valve body 68 can protrude into the cavity 89. The screw 86 has a shaft 90 which projects downwardly from the lower end of the valve body 86 and carries an annular flange 91 of larger diameter at the lower end. Two bell-shaped spring plates 92 and 92 ″ have flanges 92a and 92a ¹ and head areas 92b and 92b ¹ in which axial bores 92c and 92c ^{1 are} formed. and the shaft 90 of the screw 86 runs through the axial bores 92c and 92c ^1. A helical compression spring 93 lies in the cavity 89 of the spring housing 88 between the flange areas 92a and 92a ^{1 of} the spring plates 92 and 92 ' therefore from the lower end of the valve body 68, while the head region 9 2b ^{1 of} the spring plate 92 'is held by the protruding flange 91 of the screw 86 when the valve body 68 is designated in FIG. 3 with I and shown in FIG In addition, the valve body 68 can be moved upwards until the head area 92b ^{1 of} the spring plate 92 'against the head area 92b of the spring plate s 92 meets and the helical compression spring 93 is compressed accordingly. This position is the true in FIG. 3, denoted by II in FIG. 5 first operating position shown, in the same way, the valve body 68 is moved down until the head portion 92b of the spring plate 92 against the head portion 92b ¹ of the spring plate 92 'and the Helical compression spring 93 is compressed accordingly. This position is the second operating position, designated III in FIG. 3 and shown in FIG. 6. When the tilt valve 52 moves from the neutral position I according to FIG. 3, which is shown in FIG. 4, into the first operating position II according to FIG. 3, which is shown in FIG.

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5 is switched, a portion of the valve body 57, which is between the annular grooves 65 and 66 lies between the rings 75 and 76, so that a passage 94 is formed together with the cutouts 77 and 78 will. Furthermore, the ring 74 is located between the annular grooves 62 and 63, so that a throttled passage 95 is formed by the ring 74 and the area of the housing 57 between the grooves 62 and 63. When the tilt valve 52 is switched to the second operating position, which is designated in Fig. 3 with III and shown in Fig. 6, the ring 74 is arranged between the grooves 63 and 64, so that a further restricted passage 96 through the Ring 74 and a portion of the housing 57 between the grooves 63 and 64 is formed.

According to FIG. 3, a lift valve 97 is connected to the line 49 downstream of the tilt valve 52. The lift valve is at a standstill with the lower chamber 98 of the lifting cylinder 39 via a fourth line 99 in connection. The lower chamber 98 of the lifting cylinder 39 is used to raise and lower a carriage 34 provided with a fork (FIG. 2). A lever 100 stands with the upper end of a valve body 101 of the Lift valve 97 in connection and is movable up and down with this. The movement of the valve body is scanned by a limit switch 102, which is only then controlled by a projection 103 at the upper end of the valve body 101 is detected when the valve body 101 is raised and the lift valve 97 is in a position which can be referred to as the first operating position V. On the line 99, a throttled passage 104 is provided which serves to limit the flow of oil through the fourth line. A bypass line 105 is at one end with the fourth line 99 between the lift valve 9 7 and the throttled Passage 104 and connected at the other end to the fourth line 99 between the lifting cylinder 39 and the passage 104. In this bypass line 105 there is a back

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check valve 106, the oil towards the lower chamber 98 of the lifting cylinder 39 lets through, but blocks in the return direction. A bypass line 107 is at one end connected to the lift valve 97 and at the other end to the passages d and f of the tilt valve 52 and stands with the line 49 communicates upstream of the tilt valve 52 with a point 108. The line 49 is downstream of the lift valve 97 is connected to the latter via a first outlet line 109. A check valve 110 is located in the bypass line 107 and allows an introduction of the oil into the lift valve 97 while there is a counterflow blocked. A check valve 111 is located in the bypass line 107 between the point 108 and the tilt valve 52 and allows an introduction of the oil into the tilt valve 52 while it blocks the opposite direction. the Bypass line 107 and line 49 downstream of the lift valve 97 are connected via a pressure relief valve 112, the the oil from bypass line 107 into line 49 downstream of the lift valve 97 bypasses when the pressure of the oil in the bypass line 107 and the line 4 9 upstream of the tilt valve 52 exceeds a predetermined value, as it is due to the loading of the fork 35 (FIG. 2) of the Slide 34 can enter. The passages b and h of the tilt valve 52 are with the line 49 downstream of the Lift valve 97 in connection via a second outlet line 113, and the upper chamber 114 of the lift cylinder 39 is connected to the container 44 via a third outlet line 115.

Subsequently, the method of operation of the invention Hydraulic system are explained.

When the valve 97 is first switched from the neutral position IV to the first operating position V and the Slide 34 is to be raised, and if at the same time the tilt valve 52 is in the neutral position I, the

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Lever 100 is raised so that the limit switch 102 is switched on and the electric motor 48 starts up. The oil in the container 44 is sucked in through the suction line 45 with the aid of the hydraulic pump 57. The released oil reaches the lower chamber 98 of the lifting cylinder 39 via the line 49, the bypass line 107, the lifting valve 97 and the wide ¹ line 99 as well as the bypass line (i 10 ^r ). The piston rod 40 is therefore raised with respect to the lifting cylinder 30 and pulls the carriage 34 over the chain 4 2 upwards. While the oil flows through the bypass line 107, the check valve 110 is kept open. The check valve 106 is also open as long as the oil flows through the fourth line 99. When the lift valve 97 is switched to its second operating position VI from the first operating position V so that the carriage 34 can be lowered, and when the tilt valve 52 is at the same time in the neutral position I, the lever 100 is lowered so that the limit switch 102 the Electric motor 48 stops. The fourth line 99 is thereby brought into connection with the first line 109. In this case, the weight of the carriage 34 causes the oil to be pushed back from the lower chamber 98 of the lifting cylinder 39 into the container 44 via the line 99, the line 109, the line 49, the filter 50 and the line 51. While the oil is flowing through the line 99, the check valve 106 is closed so that the oil in the passage 104 is throttled.

When the tilt valve 52 is switched to the first operating position II according to FIG. 3, which is shown in FIG. 6, and when the lift valve 97 is in the neutral position IV, the column 33 is merely tilted backwards can be, the lever 69 is raised as shown in FIG. 3, so that the limit switch 70 is released from the finger 71 and the Electric motor 48 is turned on. The oil is sucked in through the suction line 45 with the aid of the hydraulic pump 47.

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The oil arrives from the hydraulic pump 47 via the line 49 to the tilt valve 52. This opens the check valve 111 opened in the bypass line 107, and the oil enters the annular groove 65 via the passage f and then into the forward chamber 55 of the tilt cylinder 36 via the passage 94, the annular groove 66 and the passage g as well the second line 53. As the oil passes through the passage, it is throttled. That from the hydraulic pump 47 in the rear chamber 56 of the tilt cylinder 36 introduced oil is through the line 54, the passage c, the annular Groove 60, the annular groove 59, the passage b, the conduit 113, the conduit 49, the filter 50 and the conduit 51 returned to the container 44. This causes the tilt cylinder to operate at a predetermined speed is that the column 33 is tilted backwards. During the tipping process, part of the oil gets into the Groove 52 through passage a and is then throttled to line 49 through the throttled passage 95, the groove 63 and the passage e. The throttled passage 9 5 is through the ring 74 of the valve body and a portion of the housing 57 formed between the grooves 6 2 and 63, since the ring 94 of the valve body 68 in diameter is smaller than the bore 58 and the ring 74 is located in the bore 58 between the annular grooves 62 and 63. Therefore, the pressure of the oil in the line 49 upstream of the tilt valve 52 compared to the conventional system be reduced. The pressure of the oil can be kept at the predetermined value of the check valve 112, so that the power consumption of the electric motor 48 is reduced. In addition, the noise that a pressure relief valve makes is eliminated 112 caused.

When the tilt valve 52 is then switched to its second operating position III according to FIG. 3, which is shown in FIG. 6 is, and when the lift valve 97 is in the neutral position IV and the column 33 is only tilted forward

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is to be, the lever 69 is lowered as shown in FIG. 3, so that the limit switch 70 switches on the electric motor 48. The oil is sucked in through the line 45 with the aid of the hydraulic pump 47 and reaches the tilting valve 52 via the line 49. The check valve 111 of the bypass line 107 is opened by the oil, and this passes through the Passage d into the annular groove 61 and then into the chamber 56 of the tilt cylinder 36 via the bore 58, the groove 60, the passage c and the third line 54. On the other hand, the oil discharged from the hydraulic pump 47 enters the bore 79 through the passage f, the groove 65 and the channel 83 and presses the valve body 80 against the spring force the helical compression spring 87 downwards, so that the groove 66 in connection with the groove 67 via the passage 84, the bore 79 and channel 85 arrives. The check valve 111 is opened by the oil when it passes through the bypass line 107 flows through it. The oil in the chamber 55 of the tilt cylinder 36 enters the groove 66 via the second line 53 and the passage g and flows through the passage 84, the bore 79, the channel 85 and the groove 67, the Passage h, the second line 113, the line 49 and the filter 50 and the first line 51 to the container 44 back. When passing through channel 85, the oil is throttled. This results in the tilt cylinder 36 being actuated at a predetermined speed and the column 33 tilts forward. During this tilting process, part of the oil delivered by the hydraulic pump 47 arrives through the passage a into the groove 64 and from there into the line 49 downstream of the tilt valve 52 via the throttled Passage 86, the groove 63 and the passage e. The restricted passage 96 is formed by the ring 74 of the Valve body and a portion of the housing 57 between the grooves 63 and 64, as the diameter of the ring 74 of the valve body 68 is less than that of the bore 58 and the ring 74 within the bore 78 between the grooves 63 and 64 is located. Hence the pressure of the

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Oil in the line 49 upstream of the tilt valve 4 9 compared to conventional systems. The pressure of the Oil can be kept in the relatively low value of the response pressure of the pressure relief valve 112, so that the power consumption of the electric motor 48 is restricted. Otherwise, the noise generated by the Check valve 112 is caused.

If the oil is not in the chamber 56 of the tilt cylinder 36 is initiated when the column 33 is tilted forward, since, for example, the electric motor 48 stops the valve body 80 due to the helical compression spring 87 moves upwards, so that the channel 85 through the ring 82 of the valve body 80 according to FIG. 7 is closed. This means that the oil in the chamber 55 of the lifting cylinder 36 is not released can be so that the forward tilting movement of the column 33 is stopped.

If the tilt valve 52 is then switched to the neutral position I and the lift valve 97 also in the neutral position IV is, the lever 6 9 is returned to its starting position according to FIG. 3, so that the Limit switch 70 comes into engagement with the finger 71 of the valve body 68 and the electric motor 48 is stopped. The oil does not get to the tilt cylinder 52, so that the column 33 in a desired angular position with respect to the chassis is stopped.

According to the invention, throttled passages 116 and in the case of a second embodiment according to FIGS. 8 to 10 instead of the previously mentioned throttled passages 35 and 36 may be provided.

8-10, a ring 74 'is on the valve body 5 68 instead of the ring 74, the diameter of which is essentially the same as that of the bore 58

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having. Two throttle rings 73 'and 75' are located on the valve body 68 on opposite sides of the ring 74 'and have opposite end regions 73a ¹ and 75a ¹ , the diameter of which is smaller than the bore 58. As shown in FIG. 9, the throttled passage 116 is formed by the end region 75a ^{1 of} the throttle ring 75 'and a portion of the housing 57 between the grooves 63 and 64 when the end region 75a' of the ring 75 'is in the bore 58 lies between the grooves 63 and 64 and the column 3 3 is tilted backwards. As in Fig.

10, the other throttle passage 117 is formed by the end region 73a of the ring 73 'and a portion of the housing 57 between the annular grooves 63 and 63 when the end region 73a ^{1 of} the ring 73' within the bore 58 between the grooves 62 and 63 is and the column 33 is to be tilted forward.

Otherwise, the second embodiment is essentially correct with the first embodiment according to FIGS. 4 to 7, so that further explanations are to be omitted.

Fig. 11 shows an operating position in which the oil is not in the chambers 56 of the tilt cylinder 36 moves forward during the tilting of the column 33 because, for example, the electric motor 48 has stopped. Under these circumstances, the valve body 80 is due to the action of the compression coil spring 87 moved upwards so that the channel 85 is closed by the ring 82 of the valve body 80. This means, that the oil in the chamber 55 of the tilt cylinder 36 can not be dispensed, so that the tilting movement of the Column 33 is interrupted forward.

Although it has been stated that two tilt cylinders 36 are provided for tilting the column 33 back and forth a tilt cylinder may be sufficient. However, there are preferably two guide rods on the chassis

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3 2 provided, which guide the column 33 forwards and backwards during the tilting movement.

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Claims (3)

PRIORITY: March 25, 1980, Japan, No. 38496/1980 PATENT CLAIMS 1, hydraulic system for forklifts, with one forward and backward tiltable vertical column and a fork receiving a fork which can be moved up and down on this Slide, a container for receiving oil, a suction line extending from this and connected to a hydraulic pump and one of this outgoing delivery line for oil, which is subsequently returned to the container, a on this delivery line arranged tilt valve for actuation one tilt cylinder moving the column and one disposed downstream of the tilt valve on the dispensing line 130066/0672 TER MEER · MÜLLER · STEINMEISTER Nissan Lift valve to act on a lift cylinder for the fork, characterized in that the tilt valve (52) has two throttled passages (94,95; 116,117), which allow a part of the oil to the delivery line (49) downstream of the tilt valve when this is switched to supply the oil to the tilt cylinder (36). 2. Hydraulic system according to claim 1, characterized in that the tilt valve (52) has a housing (57) with an axial bore (58) comprises that in this housing two axially spaced, connected to the bore (58), annular inlet grooves (62,64) and a corresponding outlet groove (63) are provided between the inlet grooves, that a valve body (68) is arranged displaceably in the bore (58) and has a throttle ring (74) whose diameter is smaller than that of the bore (58), and that the valve body is displaceable in such a way that the ring (74) alternatively in the region of the bore (58) between one of the input grooves and the output groove arrives. 3. Hydraulic system according to claim 1, characterized in that the tilt valve (52 ') has a housing (57) with an axially arranged bore (58) therein that comprises two annular input grooves (62,64) and one annular Exit groove (63) from the bore (58) and connect it to the outer surface of the housing (57), that a valve body (68) is slidably displaceable in the bore (58) and has a ring (74 ') on the circumference, which is essentially the same diameter as the bore (58) of the housing (57) has that two throttle rings (73 ', 75') are formed on the valve body on opposite sides of the ring (74 ¹ ), which have end portions (73a ¹ , 75a ¹ ) with reduced diameter , and that the valve body (68) is displaceable in such a way that the end sections (73a ¹ , 75a ¹ ) alternately reach the regions of the bore (58) between the inlet grooves and the outlet groove. 130066/0672