WO2012007114A2

WO2012007114A2 - Hydraulic assembly

Info

Publication number: WO2012007114A2
Application number: PCT/EP2011/003295
Authority: WO
Inventors: Stefan Arns
Original assignee: Robert Bosch Gmbh
Priority date: 2010-07-14
Filing date: 2011-07-02
Publication date: 2012-01-19
Also published as: CN102971532A; ES2573510T3; WO2012007114A3; DE102010027183A1; EP2593679B1; EP2593679A2

Abstract

The invention relates to a hydraulic assembly comprising a variable electric motor and a hydrostatic variable displacement pump which can be coupled thereto and the pivoting angle of which can be adjusted by means of a hydromechanical adjustment device, the pivoting angle being detectible by means of a pivoting angle sensor and a working pressure of the variable displacement pump being detectible by means of a pressure sensor. A speed of the electric motor can be varied depending on the pivoting angle sensor and the pressure sensor.

Description

hydraulic unit

description

The invention relates to a hydraulic unit according to the preamble of patent claim 1 and a method for operating a hydraulic unit.

In such hydraulic units with a hydraulic pump, which is driven by an electric motor, arrangements are known with constant displacement pumps. In operation with a comparatively low volume flow and comparatively high pressure, the electric motor is loaded at low rotational speeds with high torque despite low power of the hydraulic unit. It is given in such part-load operations by the ohmic losses on the electric motor, a poor efficiency of the hydraulic unit. Another disadvantage is that the cooling can be too low by a motor fan coupled to the rotational speed of the electric motor.

The document DE 10 2007 007 005 A1 shows in FIG. 3 a hydraulic unit for supplying a consumer, in which a pump is driven by an adjustable electric motor. The pump is a variable displacement pump. In this case, a hydromechanical controller for a swivel angle of the variable displacement pump and a controller for the engine speed are provided.

In a pressure-holding operation in which a certain pressure without appreciable volume flows has to be maintained by the hydraulic unit or the variable-displacement pump, the variable-displacement pump pivots back. In this case, the torque of the hydraulic unit or the electric motor is lowered, resulting in energy savings.

l A disadvantage of such hydraulic units is that the electric motor is operated in part-load operation with barely changed speed and still a significant

Has power loss.

Accordingly, the invention is based on the object to provide a hydraulic unit whose efficiency is further improved during partial load operation.

This object is achieved by a hydraulic unit having the features of patent claim 1 and by a method for its operation according to patent claim 7.

The hydraulic unit according to the invention has a controllable electric motor and a hydrostatic variable displacement pump which can be coupled thereto, the pivoting angle of which via a

hydromechanical adjusting device is adjustable. In this case, the swivel angle via a swivel angle sensor and a working pressure of the variable displacement pump via a

Pressure sensor detectable. A speed of the electric motor is dependent on the

Swivel angle sensor and the pressure sensor adjustable. Thus, the power loss of the hydraulic unit can be minimized in partial load operation. In addition, the solution for the

Retrofitting existing systems advantageous because interfaces for plant control, power and hydraulics can be used unchanged.

Further advantageous embodiments of the invention are described in the dependent claims.

It is particularly preferred if the rotational speed of the electric motor is controllable via a frequency converter. As a result, the pump can be easily switched off in the event of routine interruptions (repair, tool change, break), which leads to further energy savings.

In a preferred development, a frequency-controlled superordinate programmable logic controller is provided which is connected to the swivel angle sensor and to the pressure sensor. This can control the frequency converter.

In a preferred embodiment, the hydromechanical adjusting device is a pressure regulator or a combined pressure-flow regulator. Preferably, the electric motor is an asynchronous motor, in particular a cost-effective standard asynchronous motor.

In preferred applications, the hydraulic unit according to the invention is arranged in a machine tool - in particular in its tensioning device - or in a press or in a plastic machine - in particular plastic injection molding machine - or in a loading device for a hydraulic accumulator. In these applications, a crawl or even a standstill with maintained working pressure is often necessary, so that the energy saving potentials according to the invention are used frequently.

The method according to the invention for controlling a hydraulic unit according to one of the preceding claims has the steps:

- detecting a pressure holding operation; and

- Reduction of the speed of the electric motor.

Thus, the power loss of the hydraulic unit can be minimized in the pressure hold operation.

Detecting the pressure holding operation via the pressure sensor and the swivel angle sensor is simple in terms of apparatus technology.

It is preferred if the recognition of the pressure holding operation by reaching a predetermined working pressure and by falling below a predetermined

Swivel angle takes place.

In a preferred development of the method according to the invention, before the pressure-maintaining operation is detected, the pivoting angle is set to approximately zero. In zero-stroke operation, a qualitative and quantitative statement about wear and leakage in the hydraulic unit is possible.

In the following, various embodiments of the invention will be described in detail with reference to FIGS. Show it: Figure 1 is a hydraulic circuit diagram of a first embodiment of a hydraulic unit according to the invention; and

2 shows a hydraulic circuit diagram of a second embodiment of a hydraulic unit according to the invention.

Figure 1 shows a hydraulic circuit diagram of a first embodiment of a hydraulic unit according to the invention. It has a variable displacement pump 1, which has a

Working line 7 a (not shown) supplied to consumers. In the working line 7 an adjustable metering orifice 8 is arranged to control the consumer. The

Hydraulic unit according to the invention is operated in an open hydraulic circuit, wherein the variable displacement pump 1 via a tank line 22 sucks pressure medium from a tank T.

A swivel angle of the variable displacement pump 1 is adjusted via a pressure regulator 2. This is connected via a control line 10 with the working line 7 upstream of the metering orifice 8. Also upstream of the metering orifice 8, a pressure sensor 5 is arranged, which is connected via a signal line 12 to a frequency converter 6.

The frequency converter 6 is connected via electrical lines 14 with a variable asynchronous motor 3. The asynchronous motor 3 is connected to the variable displacement pump 1 via a shaft 16, in which a clutch 18 is arranged.

On the variable displacement pump 1, a swivel angle sensor 4 is arranged, whose output signal is transmitted via a signal line 20 to the frequency converter 6.

On the working line 7 between the variable displacement pump 1 and the metering orifice 8, a pressure limiting valve 24 is arranged, in which an effective in the closing direction

Spring force is adjustable. The pressure relief valve 24 relieves in the event of

Ansprechens the working line 7 to the tank T.

The function of the first exemplary embodiment of the hydraulic unit according to the invention according to FIG. 1 will be explained below. Depending on a load of the consumer (not shown) and a setting of the metering orifice 8, a working pressure is established in the working line 7, which is reported via the control line 10 to the pressure regulator 2. This increases the swivel angle as the working pressure decreases while decreasing it as the working pressure increases. With a reduction of the swivel angle, the delivery rate of the variable displacement pump 1 is reduced. The swivel angle is reported by the swivel angle sensor 4 via the signal line 20 to the frequency converter 6, while the working pressure is reported by the pressure sensor 5 via the signal line 12 to the frequency converter 6. This supplies the asynchronous motor 3 with electrical power as a function of the two signals.

Figure 2 shows a hydraulic circuit diagram of a second embodiment of a hydraulic unit according to the invention. In the following, only the differences from the first exemplary embodiment according to FIG. 1 will be explained.

On a comparison with the first embodiment simplified frequency converter 106 is connected via a signal line 126, a programmable logic controller. This controller 128 is superordinate to the frequency converter 106 and controls it. For this purpose, the signal line 12 connected to the pressure sensor 5 and the signal line 20 connected to the swivel angle sensor 4 are connected to the controller 128. A corresponding control signal for power control of

Asynchronous motor 3 is transmitted from the controller 128 via the signal line 126 to the frequency converter 106.

According to the invention, the following case is of particular interest: If the

hydraulic consumers (for example in a press) should not be moved or can and still be maintained in the working line 7 working pressure is maintained, the variable displacement pump 1 is swung back via the pressure regulator 2. If, in this case, the swivel angle determined by the swivel angle sensor 4 drops below a threshold value, while at the same time the working pressure determined by the pressure sensor 5 in the

Working line 7 remains above a predetermined threshold, detects the frequency converter 6 associated electronic circuit, the pressure holding operation. In a theoretical limiting case, this can also be a zero-stroke operation in which the

Variable displacement pump 1 is pivoted back to zero and no further pressure medium in the Working line 7 promotes. In this case, the previously generated working pressure is maintained in the working line 7 and leaves the consumer against his load force.

This Druckhalte- or Nullhubbetrieb is inventively detected by the sensors 4, 5, whereupon in addition to the torque in particular the speed of the

Asynchronous motor 3 is reduced.

As a result of this power reduction of the asynchronous motor 3 in the pressure-maintaining or zero-stroke operation, the hydraulic unit according to the invention saves energy.

In both embodiments shown, the variable displacement pump may be an axial piston pump or a radial piston pump.

In extruding e.g. There is a closing function for a pressing tool, which must be maintained for the entire pressing process. This takes about 50-80% of the entire cycle and requires a low flow rate at the same time high pressure. In this case, come in accordance with the prior art control oil systems

Storage charging pumps and storage systems to use. Such accumulator charge pumps are often designed for a maximum duty cycle. Thus, the

Storage charging pumps over-dimensioned for slower working cycles (eg during production changes). These storage charging pumps therefore work relatively frequently and in the

Pressure maintenance or zero stroke operation. The use of a hydraulic unit according to the invention pays off in this application example after 1 to 2 years.

Disclosed is a hydraulic unit with a controllable electric motor and with a hydrostatic variable displacement pump coupled thereto, whose pivoting angle over a

Pressure sensor detectable. A speed of the electric motor is dependent on the

Swivel angle sensor and the pressure sensor adjustable. LIST OF REFERENCE NUMBERS

1 variable pump

2 pressure regulators

3 asynchronous motor

4 swivel angle sensor

5 pressure sensor

6; 106 frequency converter

7 work management

8 metering orifice

10 control line

12 signal line

14 electrical lines

16 wave

18 clutch

20 signal line

22 tank line

24 pressure relief valve

126 signal line

128 programmable logic controller

T tank

Claims

claims

1. Hydraulic unit with a controllable electric motor (3) and with a thereto

coupled variable displacement pump (1), the pivot angle via a hydromechanical adjusting device (2) is adjustable, characterized in that the pivot angle via a pivot angle sensor (4) can be detected, and that a working pressure of the variable displacement pump (1) via a pressure sensor (5) can be detected , wherein a rotational speed of the electric motor (3) in dependence of

Swivel angle sensor (4) and the pressure sensor (5) is adjustable.

2. Hydraulic unit according to claim 1, wherein the rotational speed of the electric motor (3) via a frequency converter (6; 106) is controllable.

3. Hydraulic unit according to claim 2, with a frequency converter (106)

higher-level programmable logic controller (128) with the

Swivel angle sensor (4) and with the pressure sensor (5) is connected.

4. Hydraulic unit according to claim 1, wherein the hydromechanical adjusting device is a pressure regulator (2) or a combined pressure-flow regulator.

5. Hydraulic unit according to claim 1, wherein the electric motor is an asynchronous motor (3).

6. Hydraulic unit according to claim 1, which is arranged in a machine tool or in a press or in a plastic machine or in a charging device for a hydraulic accumulator.

7. A method for controlling a hydraulic unit according to one of the preceding claims characterized by the steps:

- detecting a pressure holding operation; and

- Reduction of the speed of the electric motor (3).

8. The method of claim 7 wherein the step of "detecting the pressure holding operation" via the pressure sensor (5) and the swivel angle sensor (4).

9. The method of claim 8, wherein the step of "detecting the pressure holding operation" by reaching a predetermined working pressure and by falling below a predetermined pivoting angle.

10. The method of claim 7 wherein prior to the step of "detecting the pressure holding operation" is carried out adjusting the pivot angle to about zero.