EP0972940A2 - Power control unit to control the hydraulic power in a drive line - Google Patents

Abstract

A control circuit for a hydraulic system has the control via a secondary circuit which takes only a fraction of the main flow and which has a direct control on the main flow control valve (5). The control loop is fed with a constant volume from the input (3) f the control system and dumps the fluid into the sump via a variable throughput flow dump valve (12). The pressure in the control loop has a direct effect on the back of the main flow control valve to maintain the required flow, by increasing the valve setting with increasing pressure in the control loop.

Description

The invention relates to a power control device for control the hydraulic power in a work line.

[State of the art]

Power control devices are already in more diverse Design known. For example, DE 35 41 750 C2 a power control device that emerges from a in the Working line arranged simple control valve exists. The pressure downstream of the control valve is tapped and returned to the control valve via a control line. Through a special design of the passage opening of the Control valve ensures that the product is high pressure and flow through the control valve a constant value is set. However, it is disadvantageous the immediate arrangement of the function function Control valve in the working line, since the control valve and in particular its opening cross-section is designed to be relatively large Need to become. There is also a risk of damage of the control valve due to cavitation with large volume flows. The control valve cannot be used as a simple slide valve be carried out because of the geometry of the opening cross section special requirements due to the power control function must meet.

One known for example from DE 196 26 793 C1 Power control device includes a so-called hyperbola controller, which has a swivel angle to a as a power control valve acting proportional valve. The One of the repercussions is the pressure in the work management the associated hydraulic pump and on the other hand by the Lever arm depends on which the pressure of the working line attacks on the pivot lever. Because of this constellation there is a hyperbolic control characteristic, d. H. at The reached regulates the maximum performance Power control device the hydraulic pump to a constant Performance, i.e. a constant product of working pressure in the Working line and delivery volume of the hydraulic pump.

However, it is assumed that the funding volume the hydraulic pump exclusively from the one through the adjustment device predetermined pivoting depends. This requirement however, only applies if the hydraulic pump runs through the drive motor is driven at a constant speed becomes. Power control devices with a hyperbola controller are therefore for drive systems with variable drive speed Not insertable. Another disadvantage is that that this power control device with the adjusting piston Adjustment device must be connected, d. H. on the adjustment device the hydraulic pump must be installed. The corresponding connection between the pivot lever and the Adjusting pistons require additional design effort. In addition, the same constructive solution cannot be found the same for all types of hydraulic pumps to be used Realize way and it is for every type of hydraulic pump a special construction is required.

OBJECT OF THE INVENTION

It is therefore the object of the present invention, a Power control device to create without one constructively complex hyperbolic regulator and one perfect function guaranteed.

The object is solved by the features of claim 1.

The invention is based on the knowledge that the Power control device is less prone to failure and the Control function is more accurate if the the power control function prescribing elements not immediately in the Work orientation but are arranged in a secondary circle. There is only one main valve in the working line, extremely simple, for example as a slide valve trained and designed for the control of large volume flows can be without this constructive difficulties prepares. From the input of the power control device according to the invention branches a branch. The secondary district becomes a constant volume flow via a flow control device supplied, in particular regardless of that in the Working pressure is high pressure. In the branch a discharge throttle is also provided, which with the valve body the main valve is connected so that its throttle cross section on the position of the valve body of the main valve depends. The invention takes advantage of the fact that the supplied Volume flow can be discharged again from the outlet throttle got to. From this continuity condition results for everyone High pressure in the work line a certain opening cross-section the outlet throttle and thus a certain secondary pressure in the secondary circuit between the current control device and the Outlet throttle. This secondary pressure becomes a first valve chamber of the main valve supplied to the valve body head for.

Opposite one on the adjustment device an adjustable one Hydropump attacking power control device with Hyperbola controller exists in the power control device according to the invention the advantage of universal applicability. In particular, the power control is independent of the Speed of the connected hydraulic pump. Furthermore, the Power control device according to the invention in any hydraulic lines at a distance from the pump Place be used as there is a mechanical reaction on the pump is not needed.

Compared to the known power control device that performance-regulating element directly in the work management, So in the main circle, there is in the invention Power control device the advantage of a simple constructive interpretation of the arranged in the work management Main valve and the more precise control function. The together the actual power control function with the current control device Takeover throttle can be relatively small be interpreted because they only have a low volume flow of Branch circuit controls. The flow control device and the flow restrictor can be combined with the main valve in one common valve block can be integrated.

The subclaims contain advantageous developments the invention.

According to claim 2, an additional proportional control valve be provided that the pressure difference between the high pressure prevailing at the entrance and the in the secondary circuit between the current control device and flow restrictor prevailing secondary pressure is applied. It can the flow control valve with one on the valve body of the main valve adjoining second valve chamber, so that the valve body of the main valve with increasing pressure difference between the high pressure and the secondary pressure in the direction to a decreasing opening cross-section of the main valve is applied. Through the proportional control valve becomes the control of the valve piston of the main valve supports and accelerates. Basically, however, it is the resetting of the valve piston of the main valve is also conceivable against exposure to the secondary pressure a return spring and the proportional control valve save. The proportional control valve can accordingly Claim 3, in particular designed as a 3/2-way valve his. The current control device preferably consists of a throttle arranged in the secondary circuit and a downstream one or limit valve arranged upstream of the throttle. The limit valve becomes corresponding Claim 4 driven by the pressure drop across the throttle. The limit valve is preferred according to claim 5 designed as a 2/2-way valve.

The flow restrictor is preferably on the valve body of the Main valve integrated according to claim 6. If that Power control valve the power in the work line is to limit a constant maximum power Open the cross section of the flow restrictor so that this is proportional to the square root of the displacement of the The valve body of the main valve rises. In addition to the realized by the power control device according to the invention Power limitation can be according to claim 9 another flow control valve and / or a pressure relief valve be provided. Before reaching the maximum Work performance of the connected hydraulic pump is working Entire device then in a flow control operation, in which the flow control valve the flow in the Working line adjusted to a constant value. At The maximum working capacity of the hydraulic pump is reached the delivery volume reduced so that the product of delivery volume and working pressure, i.e. the hydraulic power, remains constant. However, if a maximum pressure is exceeded, this is how the pressure relief valve responds.

An embodiment of the invention is described below Described in more detail with reference to the drawing. In the Show drawing:

[Examples]

Fig. 1

a hydraulic block diagram of a Embodiment of the invention Power control device;

Fig. 2

a section through an example constructive design of the invention Power control device;

Fig. 3

a view of the flow restrictor of the invention Power control device in the Viewing direction A in Fig. 2; and

Fig. 4

a section of Fig. 1 with the Designation of individual hydraulic variables, to describe the function of the power control device according to the invention required are.

Fig. 1 shows an embodiment of the invention Power control device, generally designated by the reference numeral 1 is designated. The power control device according to the invention 1 is in a working line 2 between an input 3 and an output 4 arranged. At the entrance 3 is in the embodiment shown in FIG. 1 an adjustable hydraulic pump 17 connected while on the Output 4 any consumer, for example one Hydromotor or a hydraulic working piston connected can be.

The power control device 1 according to the invention comprises a arranged in the working line 2 main valve 5, each after the position of a valve piston 6, the working line 2 releases, throttles or completely blocks.

According to the invention, a secondary circuit 7 is provided, which via a flow control device 8 with a constant volume flow is fed. The current control device 8 is over a connecting line 29 with the input 3 and thus with connected to the high pressure prevailing in the working line 2.

In the exemplary embodiment shown there is the current control device 8 from a 2/2-way valve, for example trained limit valve 9 and a downstream Throttle 10. The throttle 10 preferably has one adjustable but during the operation of the power control device 8 fixed throttle cross section. The limit valve 9 is controlled by the pressure drop across the throttle 10. If the pressure drop across the throttle 10 increases, the limiting valve 9 reduces its opening cross section. The opening cross-section of the limiting valve is reversed 9 increases when the pressure drop across the Throttle 10 reduced. This way the pressure drop kept constant at the throttle 10, resulting in a constant Volume flow leads through the flow control device 8 in the secondary circuit 7 is fed. The flow of the volume flow from the secondary circuit 7 into a pressure medium tank 11 takes place via a discharge throttle 12. The throttle cross section the flow restrictor 12 is variable and by the location of the Valve body 6 of the main valve 5 is determined. The lower the Opening cross section of the main valve 5, the smaller is also the throttle cross section of the discharge throttle 12.

The one in the secondary circuit 7 between the choke 10 of the current control device 8 and the outlet throttle 12 prevailing A secondary pressure is applied to the valve piston 6 of the main valve 5 adjacent first valve chamber 13 supplied. With increasing The valve body therefore becomes secondary pressure in the secondary circuit 7 6 of the main valve 5 in the direction of an increasing Opening cross section of the main valve 5 is applied.

Furthermore, a proportional control valve 16 is provided, which by the pressure difference between that in the working line 2 the high pressure at the entrance 3 and in the secondary circuit 7 prevailing secondary pressure is applied. If the in the secondary circuit 7 secondary pressure prevailing in the working line 2 prevailing high pressure drops, it will trained in the embodiment as a 3/2-way valve Proportional valve 16 shifted so that one on the valve body 6 of the main valve 5 adjacent second valve chamber 14 increasingly pressurized via a connecting line 15 is so that the valve body 6 of the main valve 5th increasingly in the direction of a decreasing opening cross-section the main valve 5 is acted upon. If vice versa the secondary pressure in the secondary circuit 7 compared to that in the Working line 2 prevailing high pressure rises, the second valve chamber 14 via the connecting line 15 and that Proportional control valve 16 to the pressure medium tank 11 relieved. Overall, therefore, the valve body 6 of the main valve 5 with increasing secondary pressure in the secondary circuit 7 in Fig. 1 to the left in the direction of an increasing opening cross-section of the main valve 5 and vice versa when it drops Secondary pressure in the secondary circuit 7 in Fig. 1 to the right in Direction towards a decreasing opening cross section of the main valve 5 acted upon. Basically, the second could Valve chamber 14 and the proportional control valve 16 for Simplification of the power control device according to the invention 1 also omitted and for example by a return spring be replaced.

The operation of the invention Power control device 1 is as follows:

If the high pressure in the working line 2 at the inlet 3 of the Power control device 1 increases, becomes independent of that increasing high pressure by the current control device 8 continues to be constant from the rise in high pressure independent volume flow fed into the secondary circuit 7. The outlet throttle 12, however, leaves because of the increased pressure drop to the pressure medium tank 11 briefly more volume flow drain off, as flows through the current control device 8. This leads to a decrease in the secondary pressure in the Branch circuit 7 and thus to a reduced pressure in the first valve chamber 13. At the same time, the pressure difference on the proportional control valve 16 reduced so that the second valve chamber 14 is subjected to a higher pressure becomes. Overall, the valve body 6 of the main valve 5 is in Fig. 1 to the right towards a decreasing Opening cross section of the main valve 5 shifted. Thereby the throttle cross section of the outlet throttle 12 is also reduced, since the flow restrictor 12 with the valve body 6 of the Main valve 5 is connected accordingly. Only when the outflowing volume flow with the inflowing constant Volume flow is back in equilibrium, is the equilibrium position of the valve body 6 of the main valve 5 is reached.

Conversely, if the high pressure at input 3 drops, continues through the current control device 8 to the secondary circuit 7 a constant volume flow is supplied. Because of the sinking Pressure drop is from the secondary circuit through the outlet throttle 12 7, however, for a short time compared to that of the Flow control device 8 supplied volume flow lower Volume flow discharged. This leads to an increase in pressure in the secondary circuit 7 and thus to an increase in pressure in the first valve chamber 13. Furthermore, the proportional control valve 16 moved so that the pressure in the second valve chamber 14 sinks by the second valve chamber 14 to the Pressure medium tank 11 is relieved. The valve body 6 of the main valve 5 is therefore increasing in the direction Opening cross section of the main valve 5 shifted. At the same time, the throttle cross section becomes the one with the main valve 5 coupled flow restrictor 12 increases so that a new balance between the constant fed Volume flow and the discharged volume flow.

Overall, the power control device according to the invention 1 therefore the opening cross section of the main valve 5 reduced when the high pressure in the working line 2 increases and vice versa the opening cross section of the power control device 5 increases when the high pressure in the working line 2 falls. As will be shown below, at a suitable choice of the opening cross section of the flow restrictor 12 as a function of the valve lift of the main valve 5 be achieved that the product from high pressure in the Working line 2 and from the volume flow through the main valve 5, d. H. the hydraulic power, at a constant Value is adjusted, for example the maximum power corresponds to the hydraulic pump 17.

In Fig. 1, the adjustable hydraulic pump 17 sucks from the Pressure medium tank 11 to the pressure medium and feeds it into the Working line 2 a. Serves to adjust the hydraulic pump 17 an adjusting device 18 which has a first actuating piston 19a and a first actuating cylinder 20a and a second actuating piston 19b and a second actuating cylinder 20b. In The second actuating cylinder 20b has an actuating spring 21, the hydraulic pump 17 to the maximum displacement swings out.

In addition to the power control device 1 according to the invention 1 in the embodiment shown Flow control valve 22 and a pressure relief valve 23 intended. The flow control valve 22 compares the Pressure in the working line 2 at the input 3 of the power control device 1 with the pressure at output 4 of the power control device 1, d. H. it detects the pressure drop across the Main valve 5 of the power control device 1. If this Pressure drop increases, the first actuating cylinder 20a Actuating device 18 increasingly subjected to signal pressure, so that the adjustable hydraulic pump 17 swings back. Vice versa becomes the first actuating cylinder 20a of the actuating device 18 relieved when the pressure drop across the main valve 5 drops, so that the hydraulic pump 17 to a larger displacement is swung out.

The flow control valve 22 is a pressure relief valve 23 downstream, which responds as soon as the high pressure in the Working line 2 exceeds a predetermined maximum pressure. The pressure relief valve then increases the signal pressure in the first actuating cylinder 20a of the actuating device 18 and pivots the hydraulic pump 17 back.

The power device 1 according to the invention, the flow control valve 22 and the pressure relief valve 23 work together as follows:

As long as the set power of the hydraulic pump 17 still is not reached, the hydraulic pump 17 via the Main valve 5 delivered flow through the flow control valve 22 adjusted to a constant value so that a constant flow rate to the connected consumer is fed. However, it becomes a predetermined performance reached, speaks the power control device according to the invention 1 and ensures that the product from the in the working line 2 prevailing high pressure and in the Working line 2 flowing flow a predetermined Power does not exceed. However, the permissible Maximum pressure in working line 2 exceeded, speaks the pressure relief valve 23 and swings the hydraulic pump 17 so far back that the permissible maximum pressure of the Working line 2 is not exceeded.

It should be emphasized that the power control device according to the invention 1 of course with another outer Wiring can be used. Generally serves the Power control device 1 to the power in a limit any hydraulic working line 2. The Power control device 1 according to the invention can be compact Valve assembly, therefore, also in relation to the Hydraulic pump 17 spatially distant position, for example be placed immediately in front of the consumer.

If there are several consumers arranged in parallel, each consumer can have a separate power control device 1, which is coordinated so that a permissible maximum output of the connected consumer is not exceeded.

FIG. 2 shows a constructional realization of that in FIG. 1 shown power control device 1 in a sectional view. You can see the Input 3, output 4 and a connection 30 for connection with the flow control valve 22. In an outer housing body 31, the proportional control valve 16 is integrated. In A valve piston 33 is axially displaceable in a cylinder bore 32. The valve piston 33 has a thickening 34 and two tapers 35 and 36. The valve piston 33 is with a return spring 37 biased. The axial position of the Valve piston 33 is characterized by the pressure difference between one with the inlet 3 connected first valve chamber 38 and a second valve chamber connected to the secondary circuit 7 39 and the position of the mouth of the bore 34 fixed. If the high pressure at the inlet 3 opposite the Secondary pressure in the secondary circuit 7 increases, the valve piston 33 shifted upward in Fig. 2, so that the connecting line 15 increasingly with that prevailing at the entrance 3 High pressure is applied and thus the pressure in the second valve chamber 14 of the main valve 5 rises. Vice versa becomes the second valve chamber 14 of the main valve 5 relieved when the high pressure at the inlet 3 opposite the Secondary pressure in the secondary circuit 7 drops.

The existing of the relief valve 9 and the throttle 10 Current control device 8 is located in Fig. 2 below the Inlet 3. The valve piston 40 of the limit valve 9 has two thickenings 41 and 42 and a taper 43. The limit valve 9 is connected via the connecting line 29 connected to input 3. Via two connecting lines 44 and 45 is the pressure before and after the throttle 10 detects and a first valve chamber 47 and one supplied to the second valve chamber 48. There is also a return spring 46 provided. If the pressure drop across the throttle 10 increases, the opening cross-section of the limiting valve 9 decreased. This ensures that the current control device 8 the secondary circuit 7 regardless of the high pressure supplies a constant volume flow at input 3.

The sequence from the secondary circuit 7 is via the flow restrictor 12 regulated. The outlet throttle 12 is on the valve piston 6 of the main valve 5 integrated and connects to the first Valve chamber 13 of the main valve 5. The first valve chamber 13 is via a connecting line 50 and an annular groove 51 connected to the secondary circuit 7. The flow restrictor 12 is formed in that a fixed pin 52 with a Ring body 53 cooperates and one of the valve stroke b dependent gap 54 in the exemplary embodiment releases. 3, the area of the discharge throttle 12 is in a cut representation according to the viewing direction A shown in Fig. 2 again, the ring body 53, the pin 52 and the rectangular in the embodiment Gap 54 can be seen. The gap 54 has in the embodiment a constant gap length a and one of the valve lift b dependent gap width h. The valve lift is through in FIG. 2 marked an arrow. The lowest is the result Valve stroke b when the thickening 55 of the valve body 6 the annular groove 56 in the inner housing body 57 completely closes. The largest valve stroke b results when the Annular groove 58 of the valve body 6 with the leading to the outlet 4 Annular groove 56 completely overlaps, as shown in FIG. 2 is shown.

As already stated, the geometric dependence determines the throttle opening of the discharge throttle 54 as a function of Valve strokes b the control characteristic of the invention Power control device 1. Preferably, the invention Power control device 1 operated so that this the hydraulic power to a predeterminable constant Performance limited. As shown below, this can can be achieved if at a constant gap length a gap width h (b) proportional to the valve stroke b to the square root of the valve stroke b. As from Fig. 2 too The flank of the pin 52 can therefore be recognized accordingly molded. The specified geometric relationship between the gap width h and the valve stroke b result from im following considerations.

For better clarification of those used below 4 is a section of FIG. 1 shown again enlarged and those used below mathematical quantities are illustrated there.

As explained, there is an equilibrium situation when the inflow volume flow Q corresponds _to the outflow volume flow Q _ab : Q to = Q from

The volume flow is given by the product of the opening cross-section and flow velocity, so that the following applies: Q to = A to · v to = A to 2 · Δ p ζ · α Q from = A from · V from = A from 2p x ζ · α

Where A represents _the inflow cross, A _from the outflow cross section, v _to the inflow velocity _and v the outflow velocity. The relationships used for the inflow velocity v _zu and the outflow velocity v _ab result from Bernoulli's equation of motion for incompressible liquids (cf., for example, BHJ Matthies "Introduction to Oil Hydraulics", Teubner study books, page 35). Here ζ mean the density of the pressure medium used, if α is a friction value, Δp the pressure drop at the throttle 10 and p _x the secondary pressure in the secondary circuit 7. However, the pressure in the secondary circuit 7 p _x corresponds to the pressure drop at the discharge throttle 12, since this leads directly to the pressure medium tank 11.

Under the approximation p x = p HD - Δ p ≈ p HD the following relationship applies: A to · Δ p = A from · p HD

The inflow cross section _to A and the pressure difference Ap in the Zuströmdrossel 10 are constant values. The following applies to the outflow cross section at the outflow throttle 10 A from = Ah where a is the constant gap length and h is the gap width dependent on the valve stroke b. It is essential that the valve lift b for the main valve 5 and the valve lift for the outflow throttle 12 are identical to one another, since the main valve 5 is rigidly coupled to the outlet throttle 12. If a power control is to be achieved in such a way that the product of the high pressure p _HD at the inlet 3 and the delivery volume flowing through the main valve 5 is kept constant, this corresponds to the following condition p HD · A bgr = const

Here, A _{bgr means} the limiting cross section of the main valve 5, which defines the delivery flow flowing through the main valve 5. Since the limiting cross section A _bgr depends solely on the valve stroke b due to the constant diameter of the groove 58, the following applies p HD · B = const p HD = const / b

If you put equations (9) and (6) into equation (5) you get A to · Δ p = Ah ( b ) · const b or H ( b ) ∼√ b

With the power control device 1 according to the invention, a constant power is therefore obtained if the gap width h is proportional to the square root of the valve stroke b, which can easily be achieved in the exemplary embodiment shown in FIG. 2 by a corresponding geometric configuration of the pin 52. In principle, there is the possibility of choosing the functional relationship between the gap width h or the outflow cross section A _ab and the valve lift b in a different way, as a result of which a different control characteristic of the power control device 1 according to the invention can be achieved.

The invention is not based on the illustrated embodiment limited. In particular, the gap length a must Flow restrictor 54 should not be constant. For example conceivable to use an annular throttle gap and the pin 52, for example, as a rotationally symmetrical Form body, which is easier to manufacture can be realized. The function of the radius of the rotationally symmetrical Pin 52 as a function of the valve stroke b leaves yourself either numerically or by experimenting in simple Determine way and in a numerically controlled manufacturing machine manufacture easily.

Claims (9)

Power control device (1) for controlling the hydraulic power in a working line (2) a main valve (5) arranged between an inlet (3) and an outlet (4) in the working line (2), which has a valve body (6) which, depending on its position, releases or throttles the working line (2), a flow control device (8) connected to the input (3), which feeds a constant volume flow (Q _zu ) to a secondary circuit (7), a discharge throttle (12) arranged in the secondary circuit (7), the throttle cross-section (A _ab ) of which depends on the position of the valve body (6) of the main valve (5), and a first valve chamber (13) adjoining the valve body (6) of the main valve (5), which is arranged in the secondary circuit (7) between the flow control device (8) and the discharge throttle (12) and which the valve body (6) increases with the secondary pressure (p _x ) in the secondary circuit (7) in the direction of an increasing opening cross section (A _bgr ) of the main valve (5). Power control device according to claim 1,
characterized,
that a proportional control valve (16) is provided which is dependent on the pressure difference between the high pressure (p _HD ) prevailing at the inlet (3) and the secondary pressure prevailing in the secondary circuit (7) between the flow control device (8) and the outlet throttle (12) p _x ) is applied,
the proportional control valve (16) being connected to a second valve chamber (14) adjoining the valve body (6) of the main valve (5), so that the valve body (6) of the main valve (5) increases with increasing pressure difference between the high pressure (p _HD ) and the secondary pressure (p _x ) in the direction of a decreasing opening cross section (A _bgr ) of the main valve (5) is applied. Power control device according to claim 2,
characterized,
that the proportional control valve (16) is a 3/2-way valve. Power control device according to one of claims 1 to 3,
characterized,
that the flow control device (8) consists of a throttle (10) arranged in the secondary circuit (7) and a downstream or upstream of the throttle (10) in the secondary circuit (7) arranged limiting valve (9), the limiting valve (9) from that Pressure drop at the throttle (10) is controlled. Power control device according to claim 4,
characterized,
that the limit valve (9) is a 2/2-way valve. Power control device according to one of claims 1 to 5,
characterized,
that the outlet throttle (12) is formed on the valve body (6) of the main valve (5), the throttle cross section (A _ab ) of the outlet throttle (12) increasing with increasing opening cross section (A _bgr ) of the main valve (5). Power control device according to claim 6,
characterized,
that the power control device (1) limits the power in the working line (2) to a constant power, the opening cross section (A _ab ) of the flow restrictor (12) increasing in proportion to the square root of the valve lift (b) of the main valve (5). Power control device according to one of claims 1 to 7,
characterized,
that the power control device (1) is integrated in the working line (2) of an adjustable hydraulic pump (17) and the pressure drop across the main valve (5) is used to control an adjusting device (18) of the hydraulic pump (17). Power control device according to claim 8,
characterized,
that a flow control valve (22) and / or a pressure relief valve (23) is or are arranged between the input (3) and the output (4) of the power control device (1) and the adjusting device (18).

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