Hydrostatic Assembly

Abstract

A hydrostatic assembly includes a pressure medium with a variable viscosity and a control device through which at least one process variable or state variable of the hydrostatic assembly is open-loop or closed-loop controlled as a function of the viscosity. The hydrostatic assembly further includes a temperature sensing device configured to sense a temperature of the pressure medium.

Claims

1. A hydrostatic assembly comprising: a pressure medium with a variable viscosity; at least one temperature sensing device configured to sense a temperature of the pressure medium; and a control device operably connected to the at least one temperature sensing device and configured (i) to determine the viscosity of the pressure medium as a function of the sensed temperature, (ii) to store the determined viscosity as the function of the sensed temperature, and (iii) to open-loop control and/or closed-loop control at least one process variable or state variable of the hydrostatic assembly as a function of the determined viscosity.

2. The hydrostatic assembly according to claim 1 further comprising: a pressure sensing device configured to sense a pressure of the pressure medium, wherein the control device is further configured (i) to determine the viscosity of the pressure medium as a function of the sensed pressure, and (ii) to store the determined viscosity as the function of the sensed pressure.

3. The hydrostatic assembly according to claim 1, wherein the control device is further configured to store at least one physical initial function of the determined viscosity.

4. The hydrostatic assembly according to claim 2, wherein the control device is further configured to store at least three value pairs of the determined viscosity and the sensed temperature.

5. The hydrostatic assembly according to claim 4, wherein the control device is configured to store at least one characteristic curve or one characteristic diagram of the determined viscosity as the function of the sensed temperature.

6. The hydrostatic assembly according to claim 5, wherein the control device is configured to store the at least three value pairs and/or the at least one characteristic curve or the one characteristic diagram as a reference.

7. The hydrostatic assembly according to claim 5, wherein the control device is configured to store (i) the at least three value pairs and/or the at least one characteristic curve or the one characteristic diagram for different sensed pressures, and/or (ii) a pressure-dependent correction factor of the determined viscosity.

8. The hydrostatic assembly according to claim 6 further comprising: a viscosity sensor configured for single or repeated measurement of the reference.

9. The hydrostatic assembly according to claim 8, wherein the control device is further configured to store an automatic measuring procedure for measuring the reference.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] An exemplary embodiment of a hydrostatic assembly according to the disclosure is illustrated in the drawings. The disclosure will be explained in more detail with reference to the figures of these drawings. In the drawings:

[0021] FIG. 1 shows a schematic circuit diagram of a hydrostatic assembly according to an exemplary embodiment, and

[0022] FIG. 2 shows a temperature-dependent and pressure-dependent characteristic diagram of the viscosity of a pressure medium of the assembly according to FIG. 1.

DETAILED DESCRIPTION

[0023] According to FIG. 1, a hydrostatic assembly 1 according to an exemplary embodiment has a control device 2, at least one fluid line 4, a tank T, a hydraulic machine 6, and a temperature sensing unit 8, a pressure sensing unit 10 and a viscosity sensing unit 12. The pressure sensing unit and the viscosity sensing unit 10, 12 are connected to the fluid line 4 and to the control device 2 via signal line. The temperature sensing unit 8 is connected to the tank T and to the control device 2 via a signal line. The last-mentioned is connected to the hydraulic machine 6 via a signal line. The hydraulic machine 6 is connected on its suction side to the tank T via a suction line 14. A pressure side of the hydraulic machine 6 is connected to the fluid line 4 for supplying pressure medium to a hydrostatic consumer (not illustrated). The latter is in turn connected to the tank T via a return line 16.

[0024] In an operation of the hydrostatic assembly the hydraulic machine 6 in the exemplary embodiment shown sucks in pressure medium from the tank T via the suction line 14 and feeds it to the hydrostatic consumer via the fluid line 4. The hydrostatic power of the pressure medium is then converted into mechanical power by means of said consumer. The pressure medium flows back to the tank via the return line 16.

[0025] In this context, the pressure medium is cooled again by means of a radiator of the assembly (not illustrated) in order to comply with its temperature specification. In order to pick up abrasion of the assembly occurring during the process, cleaning is continuously carried out by means of a filter of the assembly (not illustrated).

[0026] In the exemplary embodiment shown, the viscosity of the pressure medium is taken into account according to the disclosure in the open-loop or closed-loop control owing to the temperature dependence and also pressure dependence of viscosity and because of its high level of importance for fluid dynamics and power conversion.

[0027] In order to perform open-loop or closed-loop control of the hydraulic machine 6, the control device 2 is provided. A characteristic diagram 18 of the viscosity is stored therein as a function of the temperature T and of the pressure p, as shown in FIG. 2.

[0028] The control device 2 is configured in such a way that it can determine the viscosity of the pressure medium from the characteristic diagram 18 from the sensed state variables of the pressure p and temperature T, and can allow it to influence the open-loop and/or closed-loop control.

[0029] At least one dynamic open-loop and/or closed-loop control parameter is adapted to the changing viscosity either continuously or at least at defined intervals. For this purpose, a physical initial function of the viscosity is stored in the control device 2, as is known from the literature such as, for example, Murrenhoff, H., Grundlagen der Fluidtechnik [Fundamentals of Fluid Technology], Part I, hydraulics, Aachen 2001 or Helduser, S., Druckflüssigkeiten. Umdruck zur Vorlesung [Pressure fluids. Reprint for lecture], TU Dresden 1996.

[0030] One possible physical initial function which is stored in the control device 2 describes the viscosity as follows:

[00001]$\vartheta =C_1.Math.\exp .Math.\left\{\frac{C_2\left[°.Math..Math.C.\right]}{\vartheta \left[°.Math..Math.C.\right]+C_4\left[°.Math..Math.C.\right]}\right\}.Math.\exp .Math.\left\{C_3\left(p_{\mathrm{abs}}-p_{\mathrm{ref}}\right)\right\}$

[0031] FIG. 2 shows the characteristic diagram 18 according to FIG. 1. The viscosity is plotted against the temperature T. In this context, the pressure p is varied as the parameter. As the pressure rises, the viscosity also increases, while as the temperature drops the viscosity also increases. The characteristic curves of the characteristic diagram 18 are each formed from three value pairs composed of the temperature T and the assigned viscosity A characteristic diagram is illustrated here for each of three value pairs p.

[0032] A hydrostatic assembly is disclosed in which pressure medium with a variable viscosity is used for transferring power and/or for lubrication, wherein a control device is provided by means of which at least one process variable or state variable of the assembly can be open-loop and/or closed-loop controlled at least as a function of the viscosity. In addition, at least one temperature sensing device is provided by means of which a temperature of the pressure medium can be sensed. In this context, the viscosity is stored in the control device at least as a function of the temperature, said viscosity can be determined by means of the control device as a function of the sensed temperature, and can be integrated into the open-loop and/or closed-loop control by means of the control device by virtue of the fact that dynamic open-loop or closed-loop control parameters can be adapted to the changing viscosity by means of the control device.