DE3239952A1 - Hydraulic device for controlling a lifting mechanism - Google Patents

Abstract

A hydraulic device (10) for controlling a lifting mechanism in tractors is proposed which permits a reliable and quickly operating hydraulic limit position switch-off accompanied by fully hydraulic signal processing in a control circuit. In the control circuit (12) which is constructed as a complete bridge circuit and in whose bridge diagonal (38) the displacement valve (14) with its control terminals (19, 22) is located, the bridge diagonal (38) is connected to a three-way two-position control valve (41), two non-return valves (44, 49) in a first connecting line (43) and in the diagonal (38) prevent an undesired pressure compensation between the centre pressure tap-offs (36, 37) of the complete bridge circuit during the limit position switch-off but permit the desired pressure compensation in the control terminals (19, 22). The control valve (41) which is actuated by the lifting mechanism (24) in its top position controls the displacement valve (14) in such a way that it reliably moves back into its neutral position (18). <IMAGE>

Description

R. 18161

10/25/1982 My / Pi

ROBERT BOSCH GMBH, 7000 STUTTGART 1

State-of-the-art hydraulic device for hoist control

The invention is based on a hydraulic device for regulating the lifting mechanism according to the preamble of the main claim. There is already such a device from EP-A1 000 ^ 35 ^ · Well known is the fully hydraulic hoist control for a tractor with a hydraulic limit switch is equipped. To this end is in one. a control circuit designed as a full bridge circuit arranged by a power lift actuated switching valve, the relief at a predetermined limit stroke of the hoist of the control circuit to the tank is interrupted. The disadvantage here is that the switching valve is in one of the two actual value transmitters for position and tensile force leading to the tank, there is a common drainage line. This circuit for the limit switch leads to the fact that the control valve is adjusted undefined in the lowering direction and not necessarily his finds neutral position. In addition, there is a risk that the limit switch works too slowly because of the necessarily small throttles in the bridge and therefore the lifting mechanism of the working with considerable forces

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The power lift moves against a mechanical stop, but this should be avoided. In addition, it can be with this Device for the hoist control it can happen that the switching processes run too slowly during the limit switch and the directional control valve that controls the power lift, which is in a control loop, firmly throttles. The facility then works against load pressure without the power lift itself moving.

Furthermore, from DE-AS 12 "UU 363 a hydraulic device known for the control of the lifting mechanism in a tractor with a mechanically operated, pilot operated control valve as well as works with a hydraulic limit switch. A three-way two-position switching valve is already used here for the limit switch used, which is connected to the hydraulic control circuit of a main valve. Disadvantageous with this device is that it is not suitable for a fully hydraulic hoist control device because the pilot spool of the control valve is mechanically operated will. In addition, the main control slide from its basic position is only in one direction due to the control pressure medium deflectable.

Advantages of the invention

The hydraulic device according to the invention for regulating the lifting mechanism with the characterizing features of the main claim has the advantage that it is a safe and quick working final trip allowed. Pressure equalization is controlled between the control connections of the control valve, see above that the control spool is guaranteed to find its neutral position. In addition, it comes with relatively little effort in terms of

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Interconnection effort and small power requirements. before Above all, however, there is a risk that this will be in a control loop lying control valve could firmly throttle, significantly reduced.

The measures listed in the subclaims are advantageous developments and improvements of the device specified in the main claim are possible. More expedient Refinements emerge from the drawing in conjunction with the description.

drawing

An embodiment of the invention is shown in the drawing and explained in more detail in the following description. FIG. 1 shows a hydraulic device for regulating the lifting mechanism in a tractor in a simplified representation and FIG. 2 shows a part of the device according to FIG. 1 with a switching valve which is actuated upon final release and a partial Longitudinal section of the directional control valve deflected to the lowering position.

Description of the embodiment

FIG. 1 shows a device 10 for regulating the lifting mechanism in a tractor and has a hydraulic working circuit 11 and a hydraulic control circuit 12 for purely hydraulic signal processing.

The hydraulic working circuit 11 includes a pump 13, a 3/3-way valve lh working as a control valve, and a power lift 15 controlled by the latter. The directional valve k has a control slide 16 which is centered in a neutral position 18 by springs 17. By pressurizing

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impact in a first control connection 19 is the control slide 16 can be deflected into a lifting position 21 against the force of the spring. Accordingly, "when pressurized a second control connection 22 of the control slide 16 adjusted into a lowering position 23. The power lift 15 operated in a known manner a lifting arm 2U, the engages on an unspecified, usual three-point linkage of a tractor.

The hydraulic control circuit 12 is supplied with pressure medium by a control pump 25 and has a full bridge for signal processing in which a first (26) and a second bridge branch 27 are led in parallel from the control pump 25 to a tank 28. In each bridge branch 26, 27 there is a first throttle point 29 or 31 as a fixed resistor and a second, adjustable throttle point 32 or 33 in series. The second throttle point 32 in the first bridge branch 26 works as a setpoint generator for the hoist control device 10. The adjustable throttle 33 in the second bridge branch 27 works as an actual value transmitter. For this purpose it is coupled via a mechanical linkage 3 ^ - to a transmitter 35 which generates signals which are dependent on the position of the lifting arm 2h. The directional control valve 1U is connected with its control connections 19, 22 in the diagonal 38 of the full bridge. The pressure P1 at the middle pressure tap 36 between the two throttle points 29, 32 in the first bridge branch 26 thus acts in the first control connection 19 Bridge diagonal 38 in the second control connection 22 act.

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A 3/2-way switching valve Ui, which is connected essentially parallel to the bridge diagonal 38, is also arranged in the hydraulic control circuit 12 for the hydraulic end shutdown. The switching valve kl has a first connection k2 which is connected to the first control connection 1 ° and thus also to the center pressure tap 36. A first check valve kk is connected into the line k3 leading to the first connection k2 and opens to the first connection h2. A second connection U5 of the switching valve kl is connected to the second control connection 22 via a second line kS. A third connection UT of the switching valve k \ has a third line k8 connection to the center pressure tap 37. In addition, in the part of the bridge diagonal 38 between the center pressure tap 37 and the second control port 22, a second check valve k9 that opens towards the latter is connected.

The switching valve Ui receives a closing element 52 designed as a piston slide in a housing 51. The closing member 52 is held by a spring 53 in an initial position in which it blocks the first connection k2 and connects the second connection U 5 to the third connection kj. The closing element 52 can be deflected into a working position by a stop 5 fixedly connected to the lifting arm 2H against the force of the spring 53, in which the first connection k2 is connected to the second connection U 5, while the third connection U7 is hydraulically blocked is, as Figure 2 shows in more detail.

The mode of operation of the hydraulic device 10 is explained as follows:

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It is assumed that the hydraulic hoist control device 10 is in equilibrium, the actual value reported back to the second throttle point 33 being the same as that set Setpoint at the adjusting throttle 32 corresponds. The pressures P1 and P2 are the same and the control spool 16 of the directional control valve 1U is in the neutral position by its springs 17 18 centered, in which he hydraulically blocks the power lift 15.

If the second throttle point 32 is now reduced for the setpoint value for lifting, the pressure P1, which is also effective in the first control connection 19, rises and pushes the control slide of the directional valve into its lifting position 21 U to the power lift 15, which raises the lifting arm 2k further. It is now assumed that the setpoint value set at the throttle point 32 is greater than it corresponds to the uppermost position of the lifting arm 2k , the hydraulic limit switch then becoming effective. If the lifting arm 2k approaches this uppermost position, the stop 5 ^ - comes to rest on the closing element 52 of the switching valve U1 and finally moves it out of the initial position shown against the force of the spring 53 into its working position. The stop 5 ^ moves the closing member 52 to the left - in relation to FIG. 1 - until it opens the connection from the first connection ^ 2 to the second connection ^ 5. If this is the case, the pressure P1, which is higher than the pressure P2, can be released via the line ^ 3, the check valve kk , the connection controlled by the closing element 52 between the connections k2, k'5 and the second line k6 in the second connection 22 At the same time, the closing member 52 blocks the third connection Uj, so that the higher pressure P1 is neither via the switching valve k \ nor via the blocking, second check valve kg to the center pressure tap 37 in the second bridge branch 27.

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"Can build. In the control connections 1 9 ₅ 22 a pressure equalization is thus produced, so that the springs 17 move the control slide 16 in the direction of the neutral position 18. The lifting process then stops. This hydraulic limit switch is always guaranteed because the control slide 16 - can neither remain in the raised position 21 nor reach the lowered position 23. In any case, this prevents the lifting arm 2k from moving against its mechanical stop.

The closing member 52 remains in its pressed working position as long as the power lift 15 and thus the lifting arm 2k remain in the uppermost position. In order to get out of this uppermost position, the control slide of the directional control valve 1U must be brought into its lowering position 23. This can be done in that the second throttle point is opened further for the setpoint value and thus the pressure P1 drops. The same left-hand movement of the control slide 16 in the direction of the lowering position also results when the second throttle point 33 is reduced for the actual value and thus the pressure P2 is increased. In any case, the pressure P2 in the middle pressure tap 37 is greater than the pressure P1 in the first bridge branch 26. While the closing element 52 is still in its depressed working position and the third connection ^ in the switching valve! +1 is blocked, the higher one can be Build up pressure P2 from the center pressure tap 37 over a section of the bridge diagonal 38 with the opening second check valve k-9 in the second control connection 22 of the directional valve Ik . The first check valve kk in the first line k3 » prevents the higher pressure P2 from being able to decrease towards the center pressure tap 36 in the first bridge branch 26. The pressure P2 will therefore deflect the control slide of the directional valve Ik into its lowering position 23, as FIG. 2 shows. In the now running lowering process of the

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With the lifting arm 2k , the stop 5k moves away from the closing member 52, which is pushed back into its starting position by the force of the spring 53. FIG. 2 shows the beginning of this lowering process when the closing element 52 of the switching valve U1 is still pressed in the working position. The lowering process is ended when the setpoint specified at the adjustment throttle 32 corresponds to the actual value reported back at the second adjustment throttle 33. The initial situation shown in FIG. 1 is then reached again. Regardless of the hydraulic limit switch, the position of the lifting arm 2k can thus be regulated according to the signals at the setpoint generator 32 with the aid of the directional control valve 1 ^.

In the present device 10, a hydraulic limit switch can be achieved through the special arrangement of a 3/2-way valve hl and two check valves kk, k9 essentially parallel to the bridge diagonal 38 of a control circuit 12, in which the slide 16 of the directional control valve 1 k is certain Neutral position 18 finds. In addition, the hydraulic device 10 with limit switch is relatively simple and does not require any power losses.

Changes to the device 10 shown are of course possible without deviating from the concept of the invention. In this way, the actual and setpoint generators can also be interchanged in the bridge branches. Instead of of the fixed resistors 29, 31 can also occur variable throttle points. The position control shown can also be used with combined with other types of regulation or completely replaced by these. As far as possible with bridge circuits Diversity in terms of the arrangement of actual value transmitters, setpoint transmitters and fixed resistors are also other embodiments conceivable without deviating from the concept of the invention.

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Claims (3)

ε .: ι y 25-10.1982 My / Pi ROBERT BOSCH GMBH, 7000 STUTTGART 1 Expectations Π. J Hydraulic device for regulating the lifting mechanism on tractors, combine harvesters and the like, with a hydraulic working circuit with a directional control valve and a power lift and a hydraulic control circuit for hydraulic signal processing, with actual and setpoint transmitters connected to the control circuit and with additional throttling points to form the control circuit as a bridge circuit, in the diagonal of which the directional control valve, which can be pressure-actuated in two directions, is switched with its first and second control connection and with means for hydraulic end shutdown when the lifting mechanism reaches a predetermined limit stroke, for which purpose a switching valve which can be actuated by the power lift is located in the control circuit, characterized in that the switching valve as 3-way 2-position valve (^ -1) is designed, whose first connection (U2) is connected to the first control connection (19) and whose second connection (1 * 5) is connected to the second control connection (22), while the third connection ( ^ T ) is connected to the center pressure tap (3T) between two series-connected throttle points (31, 33) of a bridge branch (27) that the first connection (^ 2) has a first check valve (UH) that opens towards the latter O ΔΟΟΌ U L upstream and in the diagonal (38) between center tendrucka "handle (37) and second control connection (22) second non-return valve opening towards the latter (1 + 9) is switched. 2. Device according to claim 1, characterized in that the switching valve (U1) has a closing member (52) held in the starting position by a spring (53) which in the starting position (Figure 1) shuts off the first connection (1 + 2) and the second (1 + 5) connects to the third connection (! + T), in the deflected working position (Figure 2) with hydraulic limit shutdown the third connection {hj) is blocked and the first (1 + 2) with the second connection (1+ 5) connects. 3. Device according to claim 1 or 2, characterized in that the control circuit (12) is designed as a full bridge is and in each bridge branch (26, 27) upstream the diagonal (38) the other throttle points (29, 31) as fixed resistors and downstream of the diagonal (38) the sensors for the actual and setpoint values are designed as adjusting throttles (32, 33). k. Device according to one of Claims 1 to 3, characterized in that the control slide (16) of the directional valve (11+) has a raised position (21) when the pressure in the first control connection (19) is increased and a lowering position when the pressure is increased in the second control connection (ΐβ) (23) occupies. BATH ORIGINAL