Hydrostatic supply system for supplying a hydraulic consumer

Abstract

Hydrostatic supply device for supplying a hydraulic consumer (17), wherein the supply device comprises a hydrostatic pump (2) which is driven at variable speed by an electric motor (4), and wherein the electric motor (4) is controllable by an electronic control unit (6), wherein the control unit includes a temperature monitoring system from which a warning message can be issued and / or the drive power of the pump (2) can be limited or reduced, characterized in that a mathematical model for temperature monitoring is stored in the control unit (6), wherein the temperature monitoring system can issue a warning message after reaching a temperature increase calculated from the input variables of the control unit (6) and / or a temperature limit value, and / or the drive power of the pump (2) can be limited or reduced, wherein a specific heat capacity of the pump (2),characteristic temperature properties of a pressure medium and / or a temperature of a pressure medium in a pressure medium sink (8) immediately before operating the pump in the temporary operating zone (22) are input variables of the control unit (6).

Description

[0001] The invention relates to a hydrostatic supply device for supplying a hydraulic consumer according to the preamble of claim 1.

[0002] In known supply systems of this type, particularly when using constant-displacement pumps with internal leakage recirculation into a low-pressure chamber, reduced heat dissipation via the hydraulic fluid from the pump can lead to an impermissible temperature increase in the pump and the hydraulic fluid it contains, resulting in overheating damage to the pump. For example, the overheating can cause the lubricating film of the overheated hydraulic fluid to rupture, thus causing mechanical damage to moving parts of the pump.

[0003] To prevent such overheating damage, it is known to measure the temperature of the pressure medium in the pump and / or the pump itself, and to have the measured temperature processed by a control system. An example of such processing is shown in EP 2 818 720 A2, which, as the closest prior art, forms the basis for the preamble of claim 1. Selecting one or more suitable points to be monitored, providing the respective temperature sensors, and, last but not least, integrating the temperature sensors into the machine control system involves considerable design, equipment, and control engineering effort. This effort can increase even further when retrofitting existing systems.

[0004] DE 10 2013 006 137 A1 describes a method for controlling variable-speed displacement pumps using model-based optimization, and DE 10 2012 020 632 A1 discloses a method and a control unit for controlling a hydraulic machine. DE 10 2011 086 572 A1 discloses a method and a control device for variable-speed control of a positive displacement pump unit, as well as a positive displacement pump arrangement.

[0005] DE10 2011 010 218 A1 describes a method for controlling the pressure of a fluid conveyed by means of a speed-controlled pump.

[0006] DE 10 2008 038 436 A1 provides a method for determining a setting parameter of a hydrostatic displacement unit and a corresponding system.

[0007] DE 10 2008 063 924 A1 discloses a method for detecting faults and assigning them to fault causes in a hydrostatic system and a corresponding control unit, and DE 10 2010 015 636 A1 describes a device and a method for determining the aging state of a hydraulic fluid in a hydraulic system of a vehicle.

[0008] In contrast, the invention is based on the objective of creating a supply device or control unit in which temperature monitoring is implemented with minimal effort.

[0009] This task is solved by a supply device or control unit with the features of claim 1.

[0010] The hydrostatic supply device or control unit according to the invention serves to supply a hydraulic consumer and comprises a hydrostatic pump that can be driven at variable speeds by an electric motor. The electric motor can be controlled by an electronic control unit. According to the invention, a mathematical model for temperature monitoring is stored in the control unit, from which a warning message, in particular to a higher-level machine control system, can be output, and / or the drive power of the pump can be limited or reduced.

[0011] An advantage of the present invention is the reduced design, equipment and control engineering effort in implementing the temperature monitoring according to the invention.

[0012] Furthermore, the temperature monitoring system according to the invention can be retrofitted to existing systems with minimal effort and at low cost.

[0013] Further advantageous embodiments of the invention are described in the dependent patent claims.

[0014] Advantageously, after a time interval calculated from the input variables of the control unit, the temperature monitoring system can issue a warning message, particularly to a higher-level machine control system, and / or limit or reduce the pump's drive power. The control unit can easily determine this time interval. This allows for time-limited, critical operation of the pump within this period.

[0015] According to the invention, after reaching a temperature increase calculated from the input variables of the control unit and / or a temperature limit value, the temperature monitoring system can output a warning message, in particular to a higher-level machine control system, and / or limit or reduce the pump's drive power. The temperature increase can be determined using the mathematical model with minimal technical effort. Thus, the pump can be operated with a limited temperature increase without being damaged by an excessively high temperature rise.

[0016] Advantageously, the temperature monitoring can be deactivated, particularly when the pump is operating in a continuous operating zone. Operating the pump in this zone poses no risk of impermissible temperature increases and is therefore permissible on a permanent basis. Temperature monitoring is therefore unnecessary, but can still be performed. The continuous operating zone is preferably defined by the fact that, at a given measured pump pressure, a minimum pump speed—i.e., a pump speed exceeding a first limiting speed—is maintained, ensuring sufficient heat dissipation from the pump via the hydraulic fluid.

[0017] Preferably, temperature monitoring can be activated, particularly when the pump is operating in a temporary operating zone. In this zone, the pump can only be operated for a limited time without sustaining damage due to the resulting temperature increase. Therefore, it is advantageous to monitor the temperature of the pump and the hydraulic fluid within it in this range and, if necessary, issue a warning message, especially to a higher-level machine control system, and / or limit or reduce the pump's drive power. Typically, pressure maintenance occurs in the temporary operating zone. While the pump speed is sufficient to compensate for the pump's internal leakage, the flow rate of hydraulic fluid exiting the pump is too low to adequately dissipate the heat generated within the pump.

[0018] Advantageously, temperature monitoring can be deactivated, particularly when the pump is operating in a pressure-reduction zone. In this zone, the pump speed is insufficient at the given pump pressure to compensate for the pump's leakage rate. Therefore, operation in this zone is accompanied by a continuous decrease in pump pressure until the pump returns to the temporary operating zone due to the reduced pressure. In this temporary operating zone, temperature monitoring can be reactivated, and is typically enabled. Thus, operation in the pressure-reduction zone is limited in duration, results in the pump operating in the temporary operating zone, and therefore does not require temperature monitoring.

[0019] Advantageously, the pump's operating points are each determined by a pump pressure and a pump speed, which is specifically associated with that pump pressure. This association allows for a simple conclusion to be drawn about the pump's operating state. In particular, the operating points are determined exclusively by a pump pressure and a pump speed associated with that pump pressure.

[0020] Advantageously, the temperature monitoring can be deactivated, in particular as soon as the pump speed, which is assigned to the specific value of the pump pressure, exceeds a first limit speed. In particular, the first limit speed separates the continuous operating zone from the temporary operating zone.

[0021] Preferably, the temperature monitoring can be activated, in particular activated, as soon as the pump speed, which is assigned to the specific value of the pump pressure, falls below the first limit speed.

[0022] Advantageously, the temperature monitoring can be deactivated, in particular as soon as the pump speed, which is assigned to the specific value of the pump pressure, falls below a second limit speed, where the second limit speed is lower than the first limit speed. In particular, the second limit speed separates the temporary operating zone from the pressure reduction operating zone.

[0023] Preferably, the temperature monitoring can be activated, in particular activated, as soon as the pump speed, which is assigned to the specific value of the pump pressure, exceeds the second limit speed.

[0024] Advantageously, the pump pressure and the pump speed associated with that pressure are input variables for the control unit. Another input variable for the control unit can be the torque of the electric motor transmitted to the pump. These input variables are preferably taken into account by the mathematical model when calculating the expected temperature increase.

[0025] According to the invention, the input variables of the control unit are a specific heat capacity of the pump, characteristic temperature properties of a pressure medium, and / or the temperature of a pressure medium in a pressure medium sink immediately before the pump is operated in the temporary operating zone. The inclusion of these boundary conditions increases the accuracy of the mathematical model for temperature monitoring according to the invention.

[0026] In particular, the pump features internal leakage return, especially to a low-pressure chamber. In pumps without a leakage connection to the pressure medium sink, heat dissipation from the pump via the pressure medium is reduced, making the temperature monitoring according to the invention particularly important.

[0027] An embodiment of a supply device according to the invention is shown in the drawings. The invention will now be explained in more detail with reference to the figures in these drawings.

[0028] They show Fig. 1 a circuit diagram of a supply device according to the invention with a hydraulic consumer, and Fig. 2 a diagram of the operating zones of the supply facility according to the invention.

[0029] The in Fig. The circuit diagram shown in Figure 1 depicts a supply device 1 according to the invention with a hydrostatic pump 2, which is cost-effectively designed as an internal gear pump with internal leakage return to a low-pressure chamber. The pump 2 is driven by a speed-controlled electric motor 4, which is controlled by an electronic control unit 6. In combination with the speed-variable electric motor as the pump drive, the design of the pump 2 as a constant-speed pump is sufficient, thus reducing costs and complexity.

[0030] Pump 2 is connected to a pressure medium sink 8, and the temperature of the pressure medium in the pressure medium sink 8 is measured by a temperature sensor 10. A speed sensor 12 measures the pump speed, and a pressure sensor 14 measures the pump pressure. The measured values ​​are transmitted to the control unit 6.

[0031] A differential cylinder 17 is connected to the pump 2 via a directional valve 16.

[0032] Depending on the desired speed and direction of actuation of the differential cylinder 17, the electric motor 4 for driving the pump 2 and the directional valve 16 are controlled by the control unit 6. Particularly during pressure maintenance operation, the control unit 6 performs a target / actual comparison of the respective setpoint values ​​with the measured pump pressure and the measured pump speed.

[0033] In pressure maintenance mode, the pump speed is typically low because the differential cylinder 17 is to be kept under pressure and not moved, so that primarily only the leakage rate needs to be compensated for. However, due to the resulting low flow rate, the heat generated in pump 2 cannot be dissipated, or not completely, and can lead to an impermissible temperature increase in pump 2 and the pressure fluid it contains.

[0034] In the Fig. The diagram shown in Figure 2 depicts the operating zones of pump 2 of the supply device according to the invention, with the pump speed plotted on the X-axis and the pump pressure on the Y-axis.

[0035] In a continuous operating zone 18, which lies within a range of higher rotational speeds than a first limiting speed 20 shown in the diagram, operation of the pump 2 is safe with regard to an impermissible temperature increase and is therefore permissible on a continuous basis. The pump speed corresponding to the respective pump pressure ensures a sufficiently high flow rate in the continuous operating zone 18 to dissipate the generated heat via the hydraulic fluid. Therefore, temperature monitoring according to the invention is not required, but can nevertheless be carried out.

[0036] Pairs of values ​​for the first limiting speed 20 separate the continuous operating zone 18 from the temporary operating zone 22, which lies in a range between the pairs of values ​​for the first limiting speed 20 and a second limiting speed 24. The second limiting speed 24 is lower than the first limiting speed 20. The second limiting speed 24 is also represented as pairs of values.

[0037] The temporary operating zone 22 is a critical area for the temperature increase of pump 2 because the pump speed associated with a specific pump pressure is lower there than the pump speed associated with the same pump pressure in the continuous operating zone. Due to the lower pump speed, less heat can be dissipated from pump 2 via the hydraulic fluid, resulting in a temperature increase of pump 2. If this temperature increase persists for a certain period of time, which depends on various influencing factors, it can lead to damage to pump 2. These influencing factors include, for example, the specific heat capacity of the pump, the characteristic temperature properties of the hydraulic fluid, and / or the temperature of the hydraulic fluid in a hydraulic fluid reservoir 8 immediately before pump 2 is operated in the temporary operating zone 22. A typical operating mode for pump 2 in the temporary operating zone 22 is pressure maintenance mode.In pressure maintenance mode, the pump speed is sufficient to compensate for the leakage rate, but the resulting flow rate of the hydraulic fluid is too low to adequately dissipate the generated heat via the hydraulic fluid. Therefore, pressure maintenance mode is captured by the mathematical model and limited according to the invention, in this embodiment by time.

[0038] The second limit speed 24 separates the temporary operating zone 22 from the pressure reduction operating zone 26. In the pressure reduction operating zone 26, the pump speed corresponding to the specific pump pressure value is lower than the pump speed corresponding to the specific pump pressure value in the temporary operating zone 22. Pump 2 operation in the pressure reduction operating zone 26 is accompanied by a reduction in pump pressure until the pump pressure reaches a value within the temporary operating zone 22, where temperature monitoring can be reactivated. Alternatively, the pump pressure can be reduced by decreasing the power output of the electric motor to shift the operation of pump 2 from the pressure reduction operating zone 26 to the temporary operating zone 22.

[0039] The above will be described in more detail below using selected exemplary operating points. Fig. 2 illustrated.

[0040] A first operating point 28, located in the continuous operating zone 18, illustrates an operating state of the pump at a specific value for the pump pressure, to which a specific value for the pump speed is assigned. If, for example, during pressure maintenance operation, the pump speed is reduced while maintaining the pump pressure, an operating state is achieved that is illustrated by a second operating point 30. The pump speed has been reduced to such an extent that the second operating point lies in the temporary operating zone 22, and the temperature monitoring according to the invention is activated by the control unit 6 as soon as the pump speed, which is assigned to the specific value of the pump pressure, falls below the first limit speed 20. The temperature monitoring according to the invention is implemented as described below.

[0041] The mathematical model stored in control unit 6 calculates a time interval, based on the pump speed, pump pressure, specific heat capacity of pump 2, characteristic temperature properties of the hydraulic fluid, and the temperature of the hydraulic fluid in the hydraulic fluid reservoir 8 immediately before pump 2 is operated in temporary operating zone 22. This time interval determines how long pump 2 may operate in temporary operating zone 22 without being damaged by the temperature increase occurring there. If this time interval is reached or exceeded, the temperature monitoring system issues a warning message, for example, to a higher-level machine control system (not shown), and / or limits or reduces the drive power of pump 2. The reduction in drive power can extend to pump 2 coming to a complete standstill.As an alternative to calculating the time period, a permissible temperature increase or a permissible maximum temperature of pump 2 can be calculated.

[0042] A third operating point 32 illustrates an operating condition in which the pump speed has been further reduced for the specific pump pressure value, such that the third operating point 32 lies in the pressure reduction operating zone 26. The temperature monitoring according to the invention is deactivated by the control unit 6 as soon as the pump speed associated with the specific pump pressure value falls below the second limit speed 24. Since the pump speed is too low to maintain the set pump pressure when the pump 2 is operating in the pressure reduction operating zone 26, the pump pressure drops.

[0043] A fourth operating point 34 illustrates an operating condition in which the pump pressure has dropped or been reduced to such an extent that the fourth operating point 34 lies within the temporary operating zone 22. The temperature monitoring according to the invention is activated by the control unit 6 as soon as the pump speed, which is associated with the specific value of the pump pressure, exceeds the second limit speed 24. The temperature monitoring according to the invention is implemented as described above.

[0044] In principle, when calculating the time period during which pump 2 may be operated in the temporary operating zone 22 without being damaged by the heating taking place there, any already existing elevated temperature of pump 2 must be taken into account, which results from an immediately preceding operation of pump 2 in the temporary operating zone 22 or from a cooling phase that has not yet been completed during operation of pump 2 in the continuous operating zone 18.

[0045] The following is an example of a temperature profile during the operation of pump 2: During pressure maintenance operation in the temporary operating zone 22, the temperature of pump 2 increases over time according to ambient conditions such as pump pressure, pump speed, specific heat capacity of the pump, and initial hydraulic fluid temperature, following a characteristic curve determined by physical laws such as thermal resistances between the components involved. After increasing the pump pressure while reducing the pump speed, with pump 2 continuing to operate in the temporary operating zone 22, the temperature increase follows a different, initially steeper, characteristic curve. If the temperature increase reaches a maximum permissible value, for example, approximately 30 Kelvin, a warning message is issued by the temperature monitoring system according to the invention.To cool down and to avoid limiting or reducing the drive power of pump 2 by the control system, the operation of pump 2 can be shifted into continuous operating zone 18 by increasing the pump speed. Cooling occurs along a characteristic curve determined by physical laws such as temperature contact resistances between the components involved and the hydraulic fluid and / or between pump 2 and the ambient air.

[0046] Disclosed is a mathematical model running in conjunction with a drive control system, particularly during pressure maintenance operation of a pump, for monitoring the pump temperature in a hydrostatic supply system. The temperature monitoring system can, in particular, issue a warning message, especially to a higher-level machine control system, when a permissible operating time for the pump in a temporary operating zone, a permissible temperature increase, and / or a permissible pump temperature is reached or exceeded, and / or the pump's drive power can be limited or reduced.

[0047] Since no temperature sensors are required in the pump for the temperature monitoring according to the invention, it is applicable to all positive displacement machines. Reference symbol list 1 supply facility 2 pumps 4 electric motor 6 Control unit 8 Pressure medium sink 10 Temperature sensor 12 Speed ​​sensor 14 Pressure sensor 16 Directional valve 17 hydraulic consumers / differential cylinders 18 Continuous operating zone 20 first limiting speed 22 Temporary operating zone 24 second limiting speed 26 Pressure Reduction Operating Zone 28 first operating point 30 second operating point 32 third operating point 34 fourth operating point

Claims

[1] Hydrostatic supply device for supplying a hydraulic consumer (17), wherein the supply device comprises a hydrostatic pump (2) which can be driven at variable speeds by an electric motor (4), and wherein the electric motor (4) can be controlled by an electronic control unit (6), wherein the control unit includes temperature monitoring from which a warning message can be issued and / or from which the drive power of the pump (2) can be limited or reduced, characterized by, that a mathematical model for temperature monitoring is stored in the control unit (6), wherein the temperature monitoring system can issue a warning message after reaching an increase in temperature calculated from the input variables of the control unit (6) and / or a limit value for the temperature, and / or the drive power of the pump (2) can be limited or reduced, wherein a specific heat capacity of the pump (2), characteristic temperature properties of a pressure medium and / or a temperature of a pressure medium in a pressure medium sink (8) immediately before the operation of the pump in the temporary operating zone (22) are input variables of the control unit (6). [2] Supply device according to claim 1, wherein the temperature monitoring system can issue a warning message after the expiry of a time period calculated from the input variables of the control unit (6), and / or the drive power of the pump (2) can be limited or reduced. [3] Supply device according to one of the preceding claims, wherein the temperature monitoring can be deactivated as soon as the pump (2) is operated in a continuous operating zone (18). [4] Supply device according to one of the preceding claims, wherein the temperature monitoring can be activated as soon as the pump (2) is operated in a temporary operating zone (22). [5] Supply device according to one of the preceding claims, wherein the temperature monitoring can be deactivated as soon as the pump (2) is operated in a pressure reduction operating zone (26). [6] Supply device according to one of the preceding claims, wherein operating points of the pump (2) are each determined by a pump pressure and a pump speed. [7] Supply device according to claim 6, wherein the pump pressure and pump speed are input variables of the control unit (6). [8] Supply device according to one of the preceding claims, wherein the pump (2) has an internal leakage return.

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