EP0471166B1 - Control apparatus for regulating the delivery flow rate setting of several hydrostatic adjustable pumps - Google Patents

Description

The invention relates to a control device according to the preamble of claim 1 for controlling the delivery volume setting of several hydrostatic pumps connected in parallel to a common consumer.

From DE-PS 37 11 049 such a control device is known, each comprising a measuring and control unit assigned to the individual pumps with a pressure relief valve, a displacement transducer and a line provided with a throttle point. The latter connects the inlet of the pressure relief valve with a line connected to the working pressure line of the respective pump and leads to a spring chamber of the pilot valve designed as a 3/2-way valve. A spring in the spring chamber creates the counter pressure, which is opposed by the working pressure prevailing in the working pressure lines and in the consumer line. The displacement sensor consists of an inclined surface formed on the piston rod of the adjusting piston of the adjusting cylinder and a tracer pin which is held in contact with the inclined surface by a spring, via which it acts on the slide of the pressure relief valve. The pressure relief valve is closed to generate a correspondingly high pressure in the spring chamber when the assigned pump is set to zero delivery volume. It responds with increasing swiveling out of the pump in accordance with the movement of the inclined surface while reducing this pressure in the spring chamber. The pressure difference at the pilot valve resulting from the pressure in the spring chamber and the counteracting working pressure represents the control pressure.

Due to the pressure in the spring chamber of the pilot valve, the pressure difference counteracting the counter pressure as the setpoint of the controlled variable increases with a decreasing delivery volume of the pump to. This results in a pQ controller characteristic curve that increases with a decreasing delivery volume of the pump, which deviates from the setpoint value corresponding to the constant back pressure by the so-called permanent setpoint value deviation. Such pressure-controlled pumps have a so-called proportional behavior and consequently, inter alia, the advantage that they are adjusted to the same delivery volume setting regardless of different starting positions, ie in the case of, for example, axial piston machines at the same swivel angle, with the same setting of the back pressure; provided that their adjustment devices have the same adjustment characteristics. However, in spite of the same delivery volume setting, the delivery flows actually delivered by the individual pumps can be different, specifically because of interferences, such as different pump speeds, different structural tolerances, different friction and self-adjusting forces, and also different adjustment characteristics of the adjustment devices, etc. Another disadvantage of the known control device is also the high design effort for the measuring and control units to generate the pressure in the spring chamber of the pilot valve.

It is an object of the invention to further develop a control device of the type mentioned at the outset, with a reduction in the construction effort, so that control of the individual pumps is possible regardless of interference to the same actually conveyed flow rates.

This object is achieved by the characterizing features of claim 1.

In contrast to the prior art, instead of adjusting the delivery volume, each variable pump (swivel angle in the case of axial piston pumps) according to the invention, the delivery flow actually conveyed by each variable pump is detected by means of the respectively associated throttle, the pressure loss of which is functionally combined with the system pressure behind the throttle to the control pressure. This control pressure acts on the pilot valve assigned to the respective variable displacement pump in the direction of the control position.

Since the system pressure required in each case is automatically maintained when, for example, the flow rate of one of the variable displacement pumps is too low, by correspondingly increasing the flow rate of the other, parallel-connected variable displacement pumps, it is not necessary to take account of the design when the pilot valve is acted on. The control pressure is therefore representative of the pressure difference present at the respective throttle, a measure of the delivery flow actually conveyed by the associated variable displacement pump, so that the regulation constructed as a pressure regulation is functionally a delivery flow regulation.

Since the pressure losses at the throttles decrease with decreasing flow rate over the entire operating range and thus the system pressure increases compared to the control pressure, there is also a pQ characteristic curve increasing for all variable displacement pumps and thus a control with proportional behavior.
Differences between the flow rates actually delivered by the individual variable displacement pumps are detected by the throttling losses or, on their behalf, by the control pressures, and are compensated for by means of these pressures by correcting the delivery volume setting of the variable displacement pumps until the same flow rates are achieved. In this way, even variable size pumps can be operated so that they each have the same flow in the promote common consumer leadership. The chokes used according to the invention in order to achieve these advantages have a constructional expenditure which is negligible compared to the measuring and control units used in the prior art.

The back pressure can be in the form of a spring pressure and / or a hydraulic back pressure and can be adjustable if necessary.

Preferably, a remote control valve for controlling the hydraulic back pressure is provided, which is common to all pilot valves. In this way it is possible to apply the same back pressure to all pilot valves in order to achieve the highest accuracy of the correction of the delivery volume setting in order to achieve the same delivery rates.

According to a development of the invention, the remote control valve is designed as a pressure limiting valve, which is connected to a counterpressure control space and via a throttle point to the control pressure line of each pilot valve. Apart from the advantage of achieving the highest accuracy of the delivery volume setting, there is the possibility to shift or even change the shape of the p-Q characteristic curve for the entirety of the variable displacement pumps connected in parallel by changing the response behavior (spring pressure and spring characteristics) of the pressure relief valve. For the individual variable displacement pumps, this shift or change in shape can be achieved by adjusting the back pressure on the respective pilot valve or by changing the throttle characteristic and the flow cross section of the respective throttle.

The remote control valve can achieve the same Advantages can also be designed as a throttle element arranged in the consumer line, preferably in the form of a variable throttle valve, behind which a branch line leads to the counterpressure control chamber of each pilot valve. With this remote control valve, the control device according to the invention is not only functionally but also structurally regulated flow rate.

Fig. 1

einen Schaltplan einer Regelvorrichtung gemäß dem ersten bevorzugten Ausführungsbeispiel der Erfindung mit direkter Druckregelung (bauliche Betrachtungsweise),

Fig. 2

einen Schaltplan einer Regelvorrichtung gemäß dem zweiten bevorzugten Ausführungsbeispiel der Erfindung mit ferngesteuerter Druckregelung (bauliche Betrachtungsweise),

Fig. 3

einen Schaltplan einer Regelvorrichtung gemäß dem dritten bevorzugten Ausführungsbeispiel der Erfindung mit Förderstromregelung (bauliche Betrachtungsweise) und

Fig. 4

ein p-Q-Diagramm.

The invention is described in more detail below on the basis of three preferred exemplary embodiments with reference to the drawing. Show it

Fig. 1

2 shows a circuit diagram of a control device according to the first preferred exemplary embodiment of the invention with direct pressure control (structural view),

Fig. 2

2 shows a circuit diagram of a control device according to the second preferred exemplary embodiment of the invention with remote-controlled pressure control (structural view),

Fig. 3

a circuit diagram of a control device according to the third preferred embodiment of the invention with flow control (structural view) and

Fig. 4

a pQ diagram.

Fig. 1 shows two or more hydrostatic variable pumps 1, 2 with a flow direction, which are connected in parallel via a working pressure line 3, 4 and a suction line 5, 6 to a common consumer line 7 or to the tank 10. The consumer line 7 leads to at least one consumer (not shown). Both variable pumps 1, 2 are each via a drive shaft 8, 9 by a common or each driven by a drive motor (not shown) and drain their leak oil via a leak oil line 11, 12 connected to the tank 10. In the case of a hydrostatic transmission operating in a closed circuit, the suction lines 5, 6 can be connected to a common return line leading to the consumer instead of being connected to the tank 10.

The adjusting pumps 1, 2 are each assigned an adjusting device in the form of a hydraulic adjusting cylinder 13, 14 for adjusting their delivery volumes. In each adjusting cylinder 13, 14, an adjusting piston 15 is slidably arranged and connected via a piston rod 16 to the adjusting part 17 of the respective adjusting pump 1, 2. In each adjusting cylinder 13, 14, the adjusting piston 15 delimits a left cylinder chamber 18 with its (smaller) piston ring surface and a right cylinder chamber 19 with its (larger) piston surface. An adjustable stop 20 for limiting the stroke of the adjusting piston 15 is arranged in each cylinder chamber 18, 19. A compression spring 21 in the left cylinder chamber 18 acts on the adjusting piston 15 in the sense of a reduction in the size of the right cylinder chamber 19 and thus in the sense of a pivoting out of the variable pump 1, 2 to a larger delivery volume. The cylinder spaces 18, 19 can be pressurized via a connection.

The control of the actuating pressure of each adjusting cylinder 13, 14 takes place via a pilot valve 22, 23 in the form of a continuously adjustable 3/2-way slide valve with a connection to a first actuating pressure branch line 24 and to a second actuating pressure branch line 25. The latter line leads to the right cylinder chamber 19 of the associated adjusting cylinder 13 or 14 and is also connected via a connecting line 27 having a throttle section 26 to a tank connection line 28 leading from the pilot valve 22 or 23 to the tank 10.

The first signal pressure branch line 24 leads to a control pressure line 29, which branches off at a branch 30 from the associated working pressure line 3 or 4. Via this control pressure line 29, the slide of the pilot valve 22 or 23 is acted upon in the direction of the control position against the counter pressure p _{G of} a spring 31 arranged in a spring chamber. A control pressure line section 32 leads from the control pressure line 29 to the connection of the left cylinder chamber 18 of the associated adjusting cylinder 13 or 14. Each pilot valve 22, 23 is structurally a directly regulated pressure regulator. Each spring chamber is connected to the tank connection line for relief.

In the working pressure line 3, 4 of each variable pump 1, 2, a constant throttle 33, 34 is arranged between the branch 30 and the consumer line 7, which together with the associated pilot valve 22 or 23 represents a pressure regulator unit. The totality of all pressure regulator units forms the control device according to the invention with the following function:

The variable displacement pumps 1, 2 driven by the drive motor generate delivery flows Qi, which flow through the working pressure lines 3, 4 into the consumer line 7 and _combine there to form a total delivery flow _Qges loaded with a system pressure P _Qges . At the outlet of each variable pump 1, 2, ie upstream of the respective constant throttle 33 or 34, a pump pressure p _{Qi which is} higher than the pressure behind the throttle, ie compared to the system pressure P _Qges , increases by the pressure loss Δ p at this throttle, which acts on the respective pilot valve 22 or 23 as control pressure via the assigned control pressure line 29.

As long as the hydraulic force of this pump pressure p _{Qi is} less than the spring force of the set counter pressure P _G (setpoint of the controlled variable) Pilot valve 22 or 23 in the rest position shown in Fig. 1, in which the right cylinder chamber 19 of the adjusting cylinder 13 or 14 is connected to the tank connection line 28 leading to the tank 10 and the adjusting piston 15 by the spring 21 and the pending in the left cylinder chamber 18 Working pressure is shifted up to the stop 20 in the right cylinder chamber 19 and the variable pump 1 or 2 is swung out to the maximum delivery volume.

As soon as the hydraulic force of the pump pressure P _Qi exceeds the spring force, it moves the slide of the pilot valve 22 or 23 to the right into the control position, in which the pump pressure acts as a control pressure on the larger piston area in the right cylinder chamber 19 of the adjusting cylinder 13 or 14 and the Moving the adjusting piston 15 to the left while pivoting the adjusting pump 1 or 2 back until the force on the pilot valve 22 or 23 is balanced. The delivery flows Qi generated by the _swiveled- back variable pumps 1, 2 result in the consumer line 7 in the total delivery flow Qges required by the consumer _and loaded with the system pressure P Qges.

A maximum pump pressure P _Qi builds up at the output of each variable pump 1, 2, which is greater than the system pressure P _Qges by the pressure difference Δ p generated by the respective constant _throttle 33 or 34 and corresponds to the set counter pressure p _G or setpoint of the controlled variable . Both variable pumps 1, 2 are constantly adjusted to this setpoint of the pump pressure p _Qi and thus the corresponding system pressure p _{Qges during operation} . The assigned characteristic curves are shown in the pQ diagram according to FIG. 4. While the pump pressure characteristic curve p _{Qi runs} parallel to the x-axis, the system pressure characteristic curve p _{Qges is} a straight line that increases as the delivery volume _{setting of} the variable pumps 1, 2 decreases and the pressure difference Δ p at the constant _restrictors 33, 34 decreases. which intersects the pump pressure characteristic curve p _Qi at zero delivery volume. The ordinate difference between the two characteristic curves at each operating point represents the respective pressure difference .DELTA.p. It shows that the pump or control pressure p _Qi prevailing in the respective control pressure line 29, when viewed mathematically, consists of two components, namely the system pressure P _Qges and the Pressure difference Δ p is composed.

Due to the use of constant throttles 33, 34, each with the same throttle characteristic and setting the back pressures p _G on both pilot valves 22, 23 to the same value, both variable pumps 1, 2 are set to the same delivery volume and ideally deliver the same delivery flow; they therefore follow the same characteristic curve p _Qi or P _Qges . In practice, deviations from the ideal case that are almost unavoidable are corrected with the control device according to the invention in the following manner.

Different flow rates due to, for example, differing delivery volume settings of the variable pumps 1, 2 generate different pressure differences Δ p at the constant restrictors 33, 34. Since the system pressure P _Qges in the consumer line 7 is the same for both variable pumps 1, 2, different pump pressures P _Qi arise at the outputs of both variable pumps 1, 2, which act on the pilot valves 22, 23 as control pressures via the control pressure lines 29. As a result, the variable displacement pump with a larger flow rate and thus a larger pump pressure p _Qi or a larger pressure difference Δ p₁ is pivoted back in the direction of a smaller flow volume and the variable displacement pump with a lower flow rate and thus lower pump pressure p _Qi or smaller pressure difference Δ p₂ swung out in the direction of the maximum delivery volume until the delivery flows generated by both variable pumps 1, 2 and thus the resulting pump pressures p _Qi or pressure differences Δ p are the same without changing the total _{delivery flow} and the system pressure P _Qges .

The control device shown in FIG. 2 is provided with a remote-controlled pressure control (structural view), but is otherwise identical to the control device according to FIG. 1.

The remote-controlled pressure control comprises a remote control valve in the form of a pressure limiting valve 35, which via a remote control line 36 and a remote control branch line 37 branching from each to the spring chamber of each pilot valve 22 or 23 and via a further line 38 with a throttle point 39 to the same pilot valve 22 or 23 leading control pressure line 29 is connected.

In the case of driven variable pumps 1, 2, when the pressure relief valve 35 is closed, the pump pressure p _Qi at the outlet of each variable pump 1, 2 propagates into the respectively assigned remote control branch line 37 and the remote control line 36 and is present in the spring chamber of the respective pilot valve 22 or 23. Here it forms the counter pressure p _G together with the set spring pressure and cancels the effect of the pump pressure p _Qi on the respective pilot valve 22 or 23. As a result, both pilot valves 22, 23 remain in the rest position under the sole action of the spring pressure until the pump pressure p _Qi at the outlet of one or both variable pumps 1 or 2 opens the pressure relief valve 35 when a maximum value set on it is exceeded and the flow to the tank 10 releases. The one on the respective variable pump 1 or 2 The resulting pressure difference associated with the throttle point 39 moves the slide of the respectively assigned pilot valve 22 or 23 against the spring pressure to the right into the control position, the respective variable pump 1 or 2 being pivoted back in the manner already described until the force balance on the respective pilot valve 22 or 23 prevails. The regulation of both variable pumps 1, 2 to the same delivery flow takes place in the same way as with the directly controlled pressure control according to FIG. 1, namely by means of the control pressure p _Qi and the increasing system pressure characteristic curve with decreasing delivery volume setting.

The control device shown in FIG. 3 is provided with a flow control (structural view), but is otherwise identical to the control device according to FIG. 1.

The flow control comprises a remote control valve in the form of a variable throttle valve 40 arranged in the consumer line 7 and a branch line 41 which branches behind the variable throttle valve 40 in the direction of flow and leads via branch lines 42 to the spring chamber of each pilot valve 22, 23.

During operation, each pilot valve 22, 23 is acted upon by the pump pressure P _Qi prevailing in the associated control pressure line 29 in the direction of the control position and by the counter pressure P _G as the sum of the spring pressure and the system pressure P _Qges in the branch line 41 and the associated branch line 42 in the direction of the rest position . In this way, the pressure loss generated on each pilot valve 22, 23 by the respectively assigned constant throttle 33 or 34 as a function of the delivery flow Qi of the associated variable pump 1 or 2 and by the variable _{throttle valve} 40 as a function of the total _{delivery flow} P _{Qges acts} as a Pressure difference Δ p against the spring pressure. Since this pressure difference Δ p becomes smaller with decreasing delivery volume, there is a _{flow control} with a system pressure characteristic curve P _Qges , which also shows proportional behavior like the pressure _{controls according to FIGS} . 1 and 2 and enables the adjustment pumps 1, 2 to be regulated to the same _{flow rates} . By adjusting the variable throttle valve 40 it is achieved that the pilot valves 22, 23 assume their control position with a larger or smaller total delivery flow Qges, ie the counter pressure p _G as the setpoint of the controlled variable is changed to the same extent for all pilot valves 22, 23 and thus the system pressure Characteristic curve P _Qges shifted. A change in the throttle characteristic or the flow characteristic of the variable throttle valve 40 causes a change in the shape of the system pressure characteristic curve P _Qges .

Claims (8)

1. A control system for regulating the displacement setting of a plurality of variable-displacement hydrostatic pumps (1, 2) that are connected in parallel, each via a working pressure line (3, 4), to a consumer line (7) leading to at least one common consumer, and are each connected to a respective adjusting means (13, 14) that can be subjected to an adjusting pressure to adjust their displacement, each of the adjusting means having associated with it a pilot valve (22, 23) which, on the one hand, is acted on towards a control position by a control pressure (P_Qi) corresponding to the pressure in the working pressure line (3, 4) of the respective pump (1, 2) and taking account of the displacement setting of the pump, and, on the other hand, by a counter-pressure (P_G), whereby in the control position the setting pressure action on the adjusting means takes place in a direction towards a reduction of the displacement of the associated pump,
   characterised in that
   the control pressure (P_Qi) is taken off before a throttle (33, 34) in the working pressure line (3, 4) of the respective pump (1, 2) and acts on the associated pilot valve (22 or 23) via a control pressure line (29) towards the control position.
2. A control system according to claim 1,
   characterised in that
   each of the throttles is in the form of a constant throttle (33, 34).
3. A control system according to claim 1 or 2,
   characterised in that
   the counter-pressure (P_G) is the pressure of a spring (31) and/or a hydraulic counter-pressure acting on a counter-pressure control chamber of the respective pilot valve (22, 23).
4. A control system according to at least one of the preceding claims,
   characterised in that
   the counter-pressure (P_G) is adjustable.
5. A control system according to at least one of the preceding claims,
   characterised by a remote control valve (35, 40) common to all the pilot valves (22, 23), for controlling the hydraulic counter-pressure.
6. A control system according to claim 5,
   characterised in that
   the remote control valve is in the form of a pressure-limiting valve (35) connected to the counter-pressure control chamber and via a throttle (39) to the control pressure line (29) of each of the pilot valves (22, 23).
7. A control system according to claim 5 or 6,
   characterised in that
   the remote control valve is in the form of a throttle element (40) arranged in the consumer line (7), and behind the throttle element a branch line (41) leads to the counter-pressure control chamber of each of the pilot valves (22, 23).
8. A control system according to claim 7,
   characterised in that
   the throttle element is in the form of an adjustable throttle valve (40).

Images