GB2147053A

GB2147053A - Hydraulic control system

Info

Publication number: GB2147053A
Application number: GB08418731A
Authority: GB
Inventors: Gunther Schwerin
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1983-09-21
Filing date: 1984-07-23
Publication date: 1985-05-01
Also published as: IT1178513B; IT8422704A0; GB8418731D0; DE3334094C2; DE3334094A1; GB2147053B

Abstract

A hydraulic control system (10) for controlling a lifting mechanism on an agricultural vehicle has a proportionally acting directional control valve (11). A throttle valve (13) has a throttle slide (18) with two control chamfers (31, 29) influencing the connections from the inlet space (23) to the adjacent spaces (22, 24) and in a pressure space (21) located opposite a spring space (25) receiving the spring (26) is subjected to the pressure in the outlet space (24). When the directional control valve (11) and the following directional valve (77) operate in parallel, with pressure conditions different from one another, the throttle slide (18) always keeps constant the pressure gradient effective on the control slide (37) and the pressure gradient available for the control stream to release the shut-off unit (15), so that the proportional action of the directional control valve (11) is maintained even when there are higher load pressures on the second hydraulic motor (79). <IMAGE>

Description

SPECIFICATION Hydraulic control system The invention starts from a hydraulic control system for a working appliance driven by a hydraulic motor and attached, in particular, to an agricultural vehicle, according to the precharacterising clause of the main claim. A control system of this type is already known from German Offenlegungsschrift 3,102,505, and this has a throttle slide, a shut-off unit consisting of a shut-off valve and an associated releasing piston, and a control slide which influences the throttle slide and the releasing piston.In this control system, the control slide has formed on it an advantageous way of control edge which serves as a measuring throttle point and to which the throttle slide is assigned as a pressure balance, so that in the lifting position of a connected hydraulic motor it is possible to control the flow in that direction of a proportional pressure-medium stream independent of the load pressure. In this control device designed for an open circuit, there can be the disadvantage that the pressure-medium stream discharged to the tank by the throttle slide via a run-on chamber cannot be used to control a second additional hydraulic motor.

In particular, if both hydraulic motors were actuated simultaneously in such a case and if the following second hydraulic motor required a higher pressure than the first hydraulic motor operated by the control system, then there would arise in the control system pressure-medium conditions making it completely impossible to control the first hydraulic motor in the lifting position. Even during the lowering of the first hydraulic motor, when there is a higher pressure at the following consumer, this pressure also arises in the control chamber of the releasing piston and results in an undesirably rough action of the control system. Furthermore, it is also impossible in this control system to lower the first hydraulic motor independently of the load.In addition, this control system is expensive to construct inasmuch as a separate control line with a throttle point is necessary between the throttle slide and control slide.

A hydraulic control system is also known from German Offenlegungsschrift 3,025,949, and this has a throttle slide in addition to a shut-off unit and a control slide. In this shutoff unit consisting of a shut-off valve and releasing piston, a damping space at the releasing piston is connected to a return line in such a way that the control slide, in conjunction with the shut-off unit, allows load-compensated regulation of the lowering stream and accordingly has a proportional lowering range. Apart from the fact that, in this control system, it is not possible to regulate the lifting stream of the connected hydraulic motor independently of the load, it has, above all, the disadvantage that it is unsuitable for the simultaneous control of a following second hydraulic motor.In particular, if a following hydraulic motor were switched to pressure, whilst the first hydraulic motor controlled simultaneously by the control system is to lift, then the following hydraulic motor would~not receive any pressure medium at all. Above all, it would no longer be possible to ensure loadcompensated proportional control during the lowering of the first hydraulic motor.

Advantages of the Invention In contrast, the advantage of the control system according to the invention, having the characterising features of the main claim, is that the control system can precede a following second hydraulic motor, without its proportional action being impaired in any way.

Both during the lifting and during the lowering of the first hydraulic motor the flow of a pressure-medium stream, compensated in terms of load pressure, to or from the first hydraulic motor is controlled independently of the pressure in the second hydraulic motor. In addition, the proposed solution entails a simple construction involving a low outlay.

Advantageous developments and improvements of the control system indicated in the main claim emerge as a result of the measures listed in the sub-claims and from the description and the drawing.

Brief Description of the Drawing An exemplary embodiment of the invention is illustrated in the drawing, the single Figure of which shows a simplified representation of a control system in the lifting position.

Detailed Description of the Exemplary Embodiment The single Figure shows a control system 10 with a directional control valve 11 which is used to control the lifting mechanism of an agricultural vehicle, especially a tractor with an articulated plough.

The directional control valve 11 has a housing 1 2 in which a throttle valve 13, a control valve 1 4 and a shut-off unit 15, consisting of a shut-off valve 1 6 and an associated opening piston 17, are arranged in three axes parallel to one another.

The throttle valve 1 3 has a throttle slide 1 8 which slides in a slide bore 1 9 in the housing 12. A pressure space 21, a run-on space 22, an inlet space 23, an outlet space 24 and a spring space 25 located next to one another, as seen from left to right in relation to the Figure, are formed in the slide bore 1 9 by means of annular widened portions. The throttle slide 1 8 is subjected to a spring 26 located in the spring space 25 and to the pressures in the spring space 25 and in the pressure space 21.For this purpose, the pres sure space 21 is connected to the outlet space 24 via control channels 27 provided in the throttle slide 1 8. The spring 26 loads the throttle slide 1 8 to the left in the direction of an initial position which is not shown in any more detail and in which by means of a middle piston portion 28 the throttle slide blocks the connection between the inlet space 23 and the run-on space 22. Moreover, located in the throttle slide 1 8 is a pilot throttle 30 which is inserted between the control channels 27 and the spring space 25, so that its pressure gradient can load the throttle slide 1 8 against the spring 26.Located on the piston portion 28, on the side facing the outlet space 24, is a first control chamfer 29 which, in the initial position of the throttle slide 18, fully makes the connection between the inlet space 23 and the outlet space 24.

Moreover, the piston portion 28 has formed on it, on its other end face, a second control chamfer 31 which serves for controlling the connection between the inlet space 23 and the run-on space 22. The inlet space 23 is connected via a first line portion 32 to an inlet 33 of the directional control valve, from which a working line 34 leads to an outlet 35, the throttle valve 13, control valve 14 and shut-off valve 16 being connected in series in the working line 34. A second line portion 36 leads, as part of this working line 34, from the outlet space 24 to the following control valve 14.

The control valve 14 has a control slide 37 which is guided in a leak-proof manner and so as to slide in a second slide bore 38. Arranged in the latter (38), and again located next to one another and as seen from left to right in relation to the Figure, are a first return chamber 39, a run-off chamber 41, a control chamber 42, a first (43) and a second working chamber 44 and a second return chamber 45. The two outer return chambers 39, 45 discharge to a tank 46. The second portion 36 of the working line 34 opens into the first working chamber 43. A third line portion 47 leads, as part of the working line 34, from the second working chamber 44 to the shut-off valve 16, from which a fourth line portion 48 leads to the outlet 35. A non-return valve 49 safeguarding the second working chamber 44 is inserted in the third line portion 47.Furthermore, a return line 51 leads from the outlet 35 via the shut-off valve 1 6 to the runoff chamber 41 and on via the first return chamber 39 to the tank 46. The working line 34 and return line 51 are identical in part, namely in the region of the shut-off valve 16.

A first control line 52 leads from the control chamber 42 via a first (53) and a second throttle 54 to the second return chamber 45 and therefore on to the tank 46. The first control line 52 has, in the region between the two throttle points 53, 54, a branch 55 which feeds the particular intermediate pressure to a pressure chamber 56 assigned to the opening piston 1 7. Moreover, a second control line 57 connects the second working chamber 44 in the control valve 14 to the spring space 25 in the throttle valve 1 3.

A first control edge 58 is formed on the control slide 37 itself, in order to control the pressure-medium stream, flowing in via the working line 34, in proportion to the deflection of the control slide 37. Whereas, in the lifting position illustrated, the first control edge 58 makes the connection between the two working chambes 43, 44. in a neutral position of the control slide 37, not shown in any more detail, it breaks this connection between the working chambers. Furthermore, the control slide 37 has a second control edge 59 in order to control in a corresponding way the pressure-medium stream flowing off to the tank 46 via the return line 51.In the lifting position illustrated and in a neutral position, this second control edge 59 breaks the connection from the run-off chamber 41 to the first return chamber 39, whereas in a lowering position this connection is made in proportion to the deflection of the slide. Moreover.

the control slide 37 has a third control edge 61, by means of which it makes the connection between the first working chamber 43 and the control chamber 42 and thus influences a connection via the first control line 52 to the tank 46. In the neutral and lifting positions, this third control edge 61 blocks the connection from the working line 34 to the first control line 52, whereas in the lowering position it makes this connection. Furthermore, the control slide 37 has a fourth control edge 62, by means of which it influences the connection from the second working chamber 44 to the second return chamber 45 and thus controls the relief of pressure in the spring space 25 of the throttle valve 1 3. This fourth control edge 62 opens the connection assigned to it in the neutral and lowering positions.

In the shut-off unit 15, a damping space 63 is located opposite the pressure chamber 56 at the opening piston 1 7 and receives a spring 64 which loads the opening piston 17.

A third control line 65 leads from the damping space 63 into the return line 51 in the region between the shut-off valve 1 6 and the control slide 37. Also, the control line 65 opens into the return line 51 upstream of the non-return valve 49 in relation to the working line 34.

The single-acting hydraulic motor 66 connected to the outlet 35 of the directional control valve 11 is a power lifter which can actuate, via a lifting arm 67 and a conventional three-point linkage 68, a plough 71 articulated to the tractor frame 69.

The inlet 33 of the directional control valve 11 is supplied with pressure medium by a pump 72 via a feed line 73. In the feed line 73 there is a preceding directional valve 74 which can control an additional consumer 75.

A run-off line 76 leads from the run-on space 22 in the throttle valve 1 3 to the tank 46. Located in this run-off line 76 is a following directional valve 77 which, in the lifting position 78 illustrated, controls the pressure medium to a second hydraulic motor 79. In a manner corresponding to the preceding directional valve 74, the following directional valve 77 also has a middle position 81, making the connection to the run-off line 76, and a lowering position 82.

The control system 11 is therefore designed for an open circuit.

The mode of operation of the control system 10 is explained as follows: it may be assumed that the control slide 37 in the control valve 14 takes up a neutral position, and also the control slides of the preceding (74) and the following directional valve 77 each take up their middle position 81. The pump 72 conveys a constant pressure-medium stream via the feed line 73 into an inlet space 23. A small control stream flows out of the inlet space 23 past the throttling first control chamfer 29 into the outlet space 24 and, via the control channels 27 in the throttle slide 1 8 and via its pilot throttle 30, into the spring space 25. From there, this control oil stream passes, via the second control line 57 and the fourth control edge 62, open in the neutral position, on the control slide 37, into the second return chamber 45 and on to the tank.The pilot oil stream causes at the pilot throttle 30 a pressure gradient which presses the throttle slide 1 8 to the right, counter to the force of the spring 26, into the working position illustrated. The throttle slide 1 8 thus functions as a flow-regulating slide which keeps the control oil stream flowing off to the tank 46 constant and as low as possible and which directs most of the pressuremedium stream conveyed by the pump 72, substantially unthrottled, into the run-off line 76 and on to the tank 46. The energy losses are therefore relatively low, as long as none of the hydraulic motors is actuated.

As long as the directional control valve 11 remains in its neutral position, the consumer 75 can be lifted or lowered, as required, by means of the preceding directional valve 74.

When the following directional valve 77 is actuated, with the directional control valve 11 in the neutral position, in the lowering position 82 the connection to the run-off line 76 continues to be made. In contrast to this, when the directional valve 77 is brought into its lifting position 78, the connection to the run-off line 76 is broken, and the pressuremedium stream delivered by the pump 72 is for the most part directed to the second hydraulic motor 79. The working pressure at the second hydraulic motor 79 can rise to the maximum pressure of the pump 72, and the throttle slide 1 8 functioning as a flow-regulating slide always keeps the control oil stream flowing off to the tank constant.

It will now be assumed that the preceding (74) and the following directional valve 77 take up their respective middle positions 81, and in order to lift the plough 71, the control slide 37 in the directional control valve 11 is deflected to the left into its lifting position illustrated. By means of the fourth control edge 62 on the control slide 37, the discharge of the second control line 57 to the second return chamber 45 and to the tank 46 is interrupted. Thus, in the spring space 25 of the throttle valve 13, the spring 26 acts on the throttle slide 18, as does, in addition, the pressure of the second working chamber 44, which also builds up in the spring space 25 via the second control line 57.By means of the first control edge 58, the connection between the working chambers 43 and 44 is now made to a greater or lesser extent, so that a pressure-medium stream can flow via the working line 34, the non-return valve 49 and the shut-off valve 1 6 to the outlet 35 and on to the hydraulic motor 66. The pressure upstream of the first control edge 58 in the first working chamber 43 also prevails in the outlet space 24 of the throttle valve 1 3 and, via the control channels 27 inside the throttle slide 18, in the pressure space 21.As long as the following directional valve 77 is not actuated and the run-off line 76 discharges to the tank 46, during the lifting action of the directional control valve 11 the second control chamfer 31 will throttle the connection from the inlet space 23 to the run-on space 22 to such an extent that the pressure gradient available via the first control edge 58 corresponds to the force exerted by the spring 26 on the throttle slide 1 8 and is thus kept constant. The throttle slide 1 8 therefore functions as a pressure balance for the first control edge 58 serving as a measuring throttle point, so that load-compensated proportional lifting control of the hydraulic motor 66 is possible.

It will now be assumed that at the same time as the lifting action with the directional control valve 11 the following directional valve 77 is brought into its lifting postion 78.

During this time, the pressure-medium stream flowing in from the throttle valve 1 3 via the run-off line 76 is now supplied to the second hyraulic motor 79. As long as the working pressure in the second hydraulic motor 79 is lower than the pressure in the power lifter 66, the first control chamfer 29 on the throttle slide 1 8 remains inactive and the second control chamfer 31 throttles the connection from the inlet space 23 to the run-on space 22. The proportional control of the pressuremedium flow to the power lifter 66 is maintained unchanged.In contrast, if the pressure in the second hydraulic motor 79 exceeds the working pressure at the power lifter 66, the second control chamfer 31 opens further, whilst in the opposite way the first control chamfer 29 on the throttle slide 1 8 throttles the connection from the inlet space 23 to the outlet space 24 to an increased extent. This throttling is the greater, the more the working pressure at the second hydraulic motor 79 exceeds the working pressure of the power lifter 66. Consequently, the pressure gradient at the first control edge 58 of the control slide 37 is always kept constant, in particular so as to correspond to the force of the spring 26, so that the proportional lifting control of the power lifter 66 is not impaired.

Thus, as regards the present design of the throttle valve 1 3 in conjunction with the control valve 14, the directional control valve 11 can be used as a preceding valve in relation to the directional valve 77 with the hydraulic motor 79, and its proportional action, when the two hydraulic motors are operated in parallel, is maintained independently of the ratio of the particular working pressures to one another.

If the plough 71 is to be lowered by means of the directional control valve 11, the control slide 37 is deflected to the right, relative to the Figure, into a lowering position. At the same time, the fourth control edge 62 on the control slide 37 opens the connection from the second control line 57 to the second return chamber 45. The first control edge 58 breaks the connection between the two working chambers 43 and 44. At the same time, the third control edge 61 opens a connection from the first working chamber 43 to the control chamber 42, so that a control oil stream can flow off from the second line portion 36 into the control chamber 42 and on, via the first control line 52 with the two throttle points 53 and 54, to the tank 46.

Moreover, the connection from the run-off chamber 41 to the first return chamber 39 is made by the second control edge 59 on the control slide 37 in proportion to the deflection of the control slide 37. The intermediate pressure acting between the throttle points 53, 54 passes via the branch 55 into the pressure chamber 56, with the result that the opening piston 1 7 opens the shut-off valve 16 via a tappet. Pressure medium can then flow off from the first hydraulic motor 66 to the tank 46 via the opened shut-off valve 1 6 and the return line 51 and past the second control edge 59. At the same time, the non-return valve 49 prevents pressure medium flowing back from the hydraulic motor 66 from being able to pass into the second working chamber 44.Since the load pressure prevailing in the return line 51 is introduced into the damping chamber 63 via the third control line 65 and there acts on the opening piston 1 7 which is always subjected in its pressure chamber 56 to a constant pressure, it becomes possible by means of the shut-off unit 15 and the control valve 14 to ensure regulation of the lowering stream, compensated in terms of load pressure, as is known per se from German Offenlegungsschrift 3,025,949 mentioned in the introduction.

As long as, during lowering by means of the directional control valve 11, the following directional valve 77 assumes its middle position 81 and at the same time the run-off line 76 discharges to the tank 46, the second control chamfer 31 on the throttle slide 18 will throttle the connection to the run-on space 22 only to the extent that a pressure keeping the spring 26 in equilibrium can build up in the outer space 24. The pressure in the outlet space 24 acts via the control channel 27 in the pressure space 21, whilst the spring space 25 discharges to the tank 46 via the control slide 37. Thus, the pressure gradient available for the control oil stream via the first control line 52 is kept constant, in particular so as to correspond to the force of the spring 26.Consequently, the pressure prevailing in the pressure chamber 56 at the opening piston 1 7 is also constant. In parallel with the control oil stream flowing via the first control line 52, a relatively small control oil stream flowing to the tank 46 via the pilot throttle 30 and the second control line 57 can also form, but this does not influence the function mentioned above.

Now if, at the same time as the lowering by means of the directional control valve 11, the following directional valve 77 is brought into its lifting position 78 and the second hydrau lic motor 79 requires a higher working pressure, then the first control chamfer 29 on the throttle slide 1 8 engages to a greater extent and keeps the pressure in the outlet chamber 24 at the constant level limited by the force of the spring 26. Thus, proportional lowering control by means of the directional control valve 11 can continue undisturbed, indepen dently of the parallel actuation of the follow ing hydraulic motor 79 and its particular working pressures.

In the proposed control system 10, there fore, the directional control valve 11 can be used as a preceding valve, and its proportional action both for lifting and for lowering is maintained during parallel operation with an additional following hydraulic motor. Func tioning can thereby be achieved by relatively simple means and can take place in the constructional space available hitherto.

Of course, changes to the control system illustrated are possible, without departing from the idea of the invention. Thus, the control slide 37 can be actuated in any way.

Although the cascade arrangement is espe cially advantageous to obtain the control pres sure for the opening piston, this control pres sure can also be obtained by means of a simple on/off arrangement.

Claims

1. Hydraulic control system for a working appliance driven by a hydraulic motor and attached, in particular, to an agricultural vehicle, with a shut-off unit consisting of a shut-off valve and a releasing piston, with a control slide which controls the shut-off unit and which has a first control edge, influencing the pressure-medium stream to the hydraulic motor during lifting, and a second control edge, influencing the pressure-medium stream flowing off to the tank from the hydraulic motor during lowering, and with a throttle slide which is inserted between the control slide and an inlet of the control system into a working line guided from the inlet to an outlet of the control system via the throttle slide, the control slide and the shut-off valve, and in that (sic) the throttle slide can be subjected to a spring in a spring space located on its end face, in the direction in which the working line opens, and to a pressure difference arising at the first control edge, in the opposite direction, for which purpose a pressure space is located opposite the spring space on the throttle slide and the throttle slide has assigned to it an inlet space which is connected to a pressure-medium source and next into which are arranged on the one hand an outlet space connected into the working line and on the other hand a run-on space, and the throttle slide has two control edges controlling the connections between the spaces in opposite directions, and that (sic) in the lowering position the spring space can be discharged to the tank, as well as with a control line which braches off from the working line and can be influenced by the control slide and which is guided to the releasing piston, characterised in that the pressure-medium stream serving for controlling the releasing piston (17) is branched off from a portion (36) of the working line (34), which is located downstream of the throttle slide (18), and in that its pressure space (21) is subjected to the pressure in the outlet space (24).

2. Control system according to Claim 1, characterised in that the damping space (63) at the releasing piston (17) is connected to a region of the return line (51), which is located between the control slide (37) on the one hand and on the other hand the shut-off valve (16) and the valve means (49) which, during lowering, block the connection via the working line (34) to the throttle slide (18).

3. Control system according to Claim 1 or 2, characterised in that the first control line (52) is guided to the tank (46) via two throttle points (53, 54) connected in series, and the intermediate pressure between the two throttle points (53, 54) is supplied to the pressure chamber (56) at the releasing piston (17).

4. Control system according to one of Claims 1 to 3, characterised in that an additional directional valve (77) with a hydraulic motor (79) is inserted, downstream of the runon chamber (22), into the run-off line (76) leading away from the run-on space (22) at the throttle slide (18).

5. Control system according to one of Claims 1 to 4, characterised in that the throttle slide (18) has control channels (27) for pressure transmission and a pilot throttle (30) inserted between the outlet space (24) and the spring space (25).

6. A hydraulic control system substantially as herein described with reference to the accompanying drawing.