ES2573510T3 - Hydraulic group - Google Patents

Abstract

Hydraulic unit with an adjustable electric motor (3) and with a variable displacement pump (1) attachable to it, whose angle of rotation can be adjusted by a hydromechanical adjustment device (2) and whose effective pressure can be detected by a pressure sensor (5), characterized in that the angle of rotation can be detected by a rotation angle sensor (4), the rotation speed of the electric motor (3) being adjustable depending on the angle of rotation sensor (4) and the pressure sensor (5).

Description

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DESCRIPTION

Hydraulic group

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

In the case of hydraulic groups of this type with a hydraulic pump that is driven by an electric motor, arrangements with fixed displacement pumps are known. In the case of operation with relatively low flow volume and relatively high pressure, despite the low performance of the hydraulic group, the electric motor is charged at a lower speed with a high turning moment. In this regard, in partial load operations of this type, there is poor efficiency of the hydraulic group due to ohmic losses in the electric motor. In addition, it is disadvantageous that the cooling may be too low, in this respect, by a motor fan coupled to the rotation speed of the electric motor.

A regulation regulating the angle of rotation of a pump depending on a motor speed is already known from the patent application US 5 951 258. A regulation that controls a hydraulic valve depending on a rotation angle sensor is already known from the patent document US 4 823 552.

Publication DE 10 2007 007 005 A1 shows in Figure 3 a hydraulic group for the supply of a consumer in which a pump is driven by an adjustable electric motor. The pump is a variable displacement pump. In this regard, a hydromechanical regulator for a rotation angle of the variable displacement pump and a motor speed regulator are provided.

In a pressure maintenance operation in which a certain pressure must be maintained without considerable volume flow rates by the hydraulic group or the variable displacement pump, the variable displacement pump rotates backwards. In this regard, the turning moment of the hydraulic group or electric motor is lowered, which results in energy savings.

It is disadvantageous in hydraulic groups of this type that the electric motor is operated in partial load operation with barely modified speed and, in this respect, still has a considerable lost power.

Therefore, the invention is based on the objective of creating a hydraulic group whose efficiency is further improved in partial load operation.

This objective is solved by a hydraulic group with the characteristics of claim 1 and by a method for its operation according to claim 7.

The hydraulic group according to the invention has an adjustable electric motor and a hydrostatic variable displacement pump that can be coupled to it, whose angle of rotation can be adjusted by a hydromechanical adjustment device. In this regard, the angle of rotation can be detected by a rotation angle sensor and an effective pressure of the variable displacement pump by a pressure sensor. A speed of rotation of the electric motor is adjustable depending on the angle of rotation sensor and the pressure sensor. With this, the lost power of the hydraulic group in the partial load operation can be minimized. In addition, the solution for the retrofitting of existing facilities is advantageous, since interfaces for the control of facilities, for energy supply and for hydraulics can be used without change.

Other advantageous configurations of the invention are described in the dependent claims.

It is especially preferred if the speed of rotation of the electric motor is adjustable by a frequency converter. With this, the pump can be disconnected without problems during routine interruptions (repair, tool change, pause), which results in additional energy savings.

In a preferred refinement, a higher order stored program control is provided with respect to the frequency converter that is attached to the angle of rotation sensor and the pressure sensor. This can control the frequency converter.

In a preferred refinement, the hydromechanical adjustment equipment is a pressure regulator or a combined pressure-flow regulator.

Preferably, the electric motor is an asynchronous motor, especially an economical standard asynchronous motor.

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In preferred cases of application, the hydraulic group according to the invention is arranged in a machine tool (especially in its fastening device) or in a press or in a machine for plastics (especially plastic injection molding machine) or in a charging device for a hydraulic accumulator. In these cases of application, a slow march or even a paralysis with the effective pressure stopped is often necessary, so that the energy saving potentials according to the invention are frequently used accordingly.

The process according to the invention for the control of a hydraulic group according to one of the preceding claims has the steps:

- identification of a pressure maintenance operation; Y

- reduction of the speed of rotation of the electric motor.

With this, the lost power of the hydraulic group in the pressure maintenance operation can be minimized.

From the technical point of view, the identification of the pressure maintenance operation is carried out easily by the pressure sensor and the angle of rotation sensor.

It is preferred if the identification of the pressure maintenance operation is performed upon reaching a predetermined effective pressure and lowering below a predetermined angle of rotation.

Below, various examples of realization of the invention are described in detail by means of the Figures. They show:

Figure 1 a hydraulic circuit diagram of a first example of embodiment of a hydraulic group according to the invention; Y

Figure 2 a hydraulic circuit diagram of a second embodiment of a hydraulic group according to the invention.

Figure 1 shows a hydraulic circuit diagram of a first example of embodiment of a hydraulic group according to the invention. It has a variable displacement pump 1 that provides a consumer (not shown) with a work cable 7. In the work cable 7 there is a dosing hole 8 for the control of the consumer. The hydraulic group according to the invention is operated in an open hydraulic circuit, the variable displacement pump 1 sucking pressure means from a tank T by a tank cable 22.

An angle of rotation of the variable displacement pump 1 is adjusted by a pressure regulator 2. This is connected by a control cable 10 to the working cable 7 upstream of the dosing hole 8. Also upstream of the dosing hole 8 A pressure sensor 5 is arranged which is connected to a frequency converter 6 by a signal cable 12.

The frequency converter 6 is connected to an asynchronous motor 3 adjustable by electric cables 14. The asynchronous motor 3 is connected to the variable displacement pump 1 by a wave 16 in which a coupling 18 is arranged.

In the variable displacement pump 1, a rotation angle sensor 4 is arranged, whose output signal is transmitted to the frequency converter 6 by a signal cable 20.

In the working cable 7 between the variable displacement pump 1 and the dosing port 8, a pressure relief valve 24 is arranged in which an effective spring force can be adjusted in the closing direction. The pressure relief valve 24 discharges the working cable 7 to the tank T in the case of a response.

Next, the function of the first embodiment of the hydraulic group according to the invention according to Figure 1 is explained.

Depending on a load of the consumer (not shown) and an adjustment of the dosing hole 8, an effective pressure appears on the work cable 7 which is communicated by the control cable 10 to the pressure regulator 2. This increases the angle of turn in the case of diminishing effective pressure, while reducing it in the case of increasing effective pressure. In the case of a reduction in the angle of rotation, the volumetric capacity of the variable displacement pump 1 is reduced. The angle of rotation is communicated from the angle of rotation sensor 4 by the signal cable 20 to the frequency converter 6, while the effective pressure is communicated from the pressure sensor 5 by the signal cable 12 to the frequency converter 6. It provides electrical power to the synchronous motor 3

depending on both signals.

Figure 2 shows a hydraulic circuit diagram of a second embodiment of a hydraulic group according to the invention. In this regard, only the differences with respect to the first embodiment according to Figure 1 are explained below.

5 A program control stored by a signal cable 126 is connected to a simplified frequency converter 106 in comparison with the first embodiment. This control 128 is arranged in a higher order with respect to the frequency converter 106 and controls it. For this, the signal cable 12 connected to the pressure sensor 5 and the signal cable 20 connected to the angle of rotation sensor 4 are connected to the control 128. A control signal corresponding to the power regulator of the asynchronous motor 3 is transmitted from control 128 by 10 signal cable 126 to frequency converter 106.

According to the invention, the following case is especially interesting: If the hydraulic consumer should not or cannot continue moving (for example, in a press) and even so! The effective pressure obtained in the working cable 7 must be maintained integrally, the variable displacement pump 1 is turned backwards by the pressure regulator 2. In this respect, if the rotation angle calculated by the rotation angle sensor 4 drops 15 below a threshold value while simultaneously the effective pressure calculated by the pressure sensor 5 on the work cable 7 remains above a predetermined threshold value, an electronic circuit assigned to the frequency converter 6 identifies the maintenance operation of the pressure. In an extreme theoretical case, this can also be a zero stroke operation in which the variable displacement pump 1 is turned back to zero and no additional means of pressure is extracted on the work cable 7. In this respect , the previously generated effective pressure remains maintained in the work cable 7 and allows the consumer to persist against its load force.

This operation of maintaining the pressure or zero stroke is identified, according to the invention, by the sensors 4, 5, whereby in addition to the turning moment, the rotation speed of the asynchronous motor 3 is also reduced.

25 By this reduction of power of the asynchronous motor 3 in the maintenance operation of the pressure or zero stroke, the hydraulic group according to the invention saves energy.

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

In the case of extrusion presses, for example, there is a closing function for a pressing tool that has to be maintained integrally for the entire pressing process. This lasts approximately 50-80% of the entire cycle and, in this regard, requires a low extra amount in the case of simultaneously high pressure. In this regard, according to the state of the art, control oil systems with accumulator charge pumps and accumulator systems are used. Accumulator charge pumps of this type are often designed for a maximum duty cycle. Therefore, the accumulator charge pumps are oversized for slower duty cycles (for example, in the case of production changes). Therefore, these accumulator charge pumps operate relatively frequently and in zero pressure or run maintenance operation. The use of a hydraulic group according to the invention is profitable in the case of this application example after 1 or 2 years.

A hydraulic group with an adjustable electric motor and with a hydrostatic variable displacement pump 40 coupled to it, whose rotation angle can be adjusted by a hydromechanical adjustment equipment, is revealed. In this regard, the angle of rotation can be detected by a rotation angle sensor and an effective pressure of the variable displacement pump by a pressure sensor. A speed of rotation of the electric motor is adjustable depending on the angle of rotation sensor and the pressure sensor.

Reference List

Four. Five

 one

 variable displacement pump

 2

 pressure regulator

 3

 asynchronous motor

 4

 angle of rotation sensor

 5

 pressure sensor

 6; 106

 frequency converter

 7

 work cable

 8

 dosage hole

 10

 control cable

 12

 signal cable

 14

 electric cables

 16 18 20 5 22 24 126 128

 wave coupling signal cable tank cable pressure relief valve signal cable program control stored

 T 10

 tank

Claims (9)

5 10 fifteen twenty 25 1. Hydraulic unit with an adjustable electric motor (3) and with a variable displacement pump (1) attachable to it, whose angle of rotation can be adjusted by a hydromechanical adjustment device (2) and whose effective pressure can be detected by a sensor pressure (5), characterized in that the angle of rotation can be detected by a rotation angle sensor (4), the speed of rotation of the electric motor (3) being adjustable depending on the angle of rotation sensor (4) and the sensor of pressure (5). 2. Hydraulic group according to claim 1, the speed of rotation of the electric motor (3) being adjustable by a frequency converter (6; 106). 3. Hydraulic group according to claim 2, with a higher order stored program control (128) with respect to the frequency converter (106) that is connected to the angle of rotation sensor (4) and the pressure sensor (5). 4. Hydraulic group according to claim 1, the hydromechanical adjustment equipment being a pressure regulator (2) or a combined pressure-flow regulator. 5. Hydraulic group according to claim 1, the electric motor being an asynchronous motor (3). 6. Hydraulic group according to claim 1, which is arranged in a machine tool or in a press or in a machine for plastics or a charging device for a hydraulic accumulator. 7. Method for controlling a hydraulic group according to one of the preceding claims, characterized by the steps: - identification of a pressure maintenance operation; Y - reduction of the speed of rotation of the electric motor (3). 8. Procedure according to claim 7, performing the step "identification of the operation of pressure maintenance "by the pressure sensor (5) and the angle of rotation sensor (4). 9. Procedure according to claim 8, performing the step "identification of the operation of pressure maintenance "upon reaching a predetermined effective pressure and lowering below a predetermined angle of rotation.