Device for filter condition detection

Abstract

Device for filter condition detection in a mobile hydraulic system, comprising a tank (18) for receiving hydraulic fluid, a temperature sensor (36) for measuring the temperature of the hydraulic fluid, a filter (26), a pump (16) driven by an electric motor (14) for pumping the hydraulic fluid from the tank (18) through the filter (26) to a consumer (10), and a lockable return path (28) connecting the outlet of the filter (26) to the tank (18), characterized by a controller (32) for controlling the speed of the motor (14), a measuring device (34) for measuring the current consumption (I) of the motor (14), and a control device (38) for evaluating pairs of values ​​of temperature (T) and current consumption (I).

Description

[0001] The invention relates to a device for filter condition detection in a mobile hydraulic system, comprising a tank for receiving hydraulic fluid, a temperature sensor for measuring the temperature of the hydraulic fluid, a filter, a pump driven by an electric motor for pumping the hydraulic fluid from the tank through the filter to a consumer, and a lockable return path that connects the outlet of the filter to the tank.

[0002] A mobile hydraulic system could, for example, be a hydraulic unit for a spring-applied brake in a rail vehicle. Since the available installation space in such rail vehicles is usually limited, the entire hydraulic system should be designed to be as compact as possible.

[0003] The filter, usually a depth filter, serves to separate foreign substances from the hydraulic fluid. As the trapped particles accumulate in the filter, its flow resistance increases over time. It is therefore necessary to check the condition of the filter periodically and replace it if necessary.

[0004] From DE 10 2016 215 909 A1, a device for filter condition detection is known in which the filter condition is evaluated based on the switching point of a pressure switch as a function of temperature. Other publications, for example DE 10 2022 200 673 B3, describe detection devices in which the differential pressure between the inlet and outlet sides of the filter is measured using at least one pressure sensor.

[0005] These known detection devices require the use of at least one additional measuring device, which would not be needed for the regular operation of the hydraulic system (without filter detection), for example a differential pressure sensor, which increases the required installation space.

[0006] The object of the invention is to create a filter detection device that is characterized by a small footprint.

[0007] This problem is solved according to the invention by a filter detection device characterized by a controller for regulating the speed of the motor, a measuring device for measuring the current consumption of the motor, and a control device for evaluating pairs of values ​​of temperature and current consumption.

[0008] To check the filter condition, the return path is opened, resulting in a low pressure at the filter outlet, influenced by the flow resistance of the return path. Due to the low pressure, the potential flow rate in the path to the consumer is negligible. Since the pump drive speed is regulated to a constant value, a constant flow rate is established. At a given temperature, the current draw of the pump drive is then a monotonically increasing function of the flow resistance in the filter, making the current draw as a function of temperature a good indicator of the filter's loading level.

[0009] A significant advantage of the device according to the invention is that no additional hydraulic components are required. The necessary electronic components, for example the controller and the current measuring device, can be designed to be very compact and can be fully or partially integrated into the motor.

[0010] Advantageous embodiments of the invention are specified in the dependent claims.

[0011] The motor can be a brushless, i.e., electronically commutated motor, which drives the pump at a regulated speed.

[0012] To enable the pump to start without pressure, a switching valve is usually arranged in the return path. This valve opens before the pump drive is switched on and is then held open for a period corresponding to the pump's start-up phase. The control unit of the device according to the invention can be designed to measure the current consumption of the pump drive towards the end of this start-up phase, as soon as the pump speed has stabilized.

[0013] An electronic memory in the control unit can store a curve indicating the relationship between current draw and temperature for a new filter. When checking the filter's condition, the measured current draw is compared to the value stored for the currently measured temperature of the hydraulic fluid. If the difference exceeds a certain threshold, a warning signal can be automatically issued, for example, in the form of a visual or audible indicator, informing personnel that the filter needs to be replaced. Alternatively, the control unit can also electronically store measurement results obtained at different temperatures, allowing a curve representing the filter's current condition to be retrieved periodically.

[0014] The following section explains an exemplary embodiment in more detail with reference to the drawings. They show: Fig. 1 a hydraulic diagram and an electrical circuit diagram of a hydraulic system with a device according to the invention for filter state detection; Fig. 2 curves showing the current consumption of a pump drive as a function of temperature for a new filter and a partially loaded filter; and Fig. 3 A flowchart for a measurement process.

[0015] Fig. Figure 1 shows the essential components of a hydraulic system for supplying pressure to a pressure regulator 10, which regulates the hydraulic pressure in a spring-applied brake B of a rail vehicle. A pump 16, driven by a motor 14, draws hydraulic fluid from a tank 18 and delivers it via a check valve 20 to a pressure accumulator 22, which provides the pressure for the pressure regulator 10. A pressure relief valve 24, connected between the pressure accumulator 22 and the tank 18, limits the pressure in the pressure accumulator 22 to a mechanically adjustable value.

[0016] In the hydraulic path from the outlet of pump 16 to the check valve 20, a filter 26, for example a depth filter, is arranged to limit particle contamination of the hydraulic fluid. From the outlet of filter 26, a return path 28, which can be shut off by a switching valve 30, leads back to tank 18.

[0017] In this example, motor 14 is a brushless motor. A corresponding motor driver MT is connected to a DC voltage source U and includes an integrated controller 32 for regulating the motor speed and a measuring device 34 for measuring the current consumption of motor 14. A device for filter condition detection comprises, in addition to the controller 32 and the measuring device 34, a temperature sensor 36 for measuring the temperature of the hydraulic fluid in tank 18 and an electronic control unit 38 configured to control the measuring device 34 and the temperature sensor 36 and to query measured values. The control unit 38 also controls the switching valve 30.

[0018] The switching valve 30 is normally closed (NC) and is therefore in the closed position when pump 16 is switched off. When a command is given to switch on the pump, the valve opens, thus ensuring that pump 16 can start without pressure. During the pump's start-up phase, the speed of the pump drive 14 is regulated to a constant value by the controller 32. Since the return path 28 is open, almost the entire pump flow rate flows through this path. Under these conditions, a constant flow rate through the filter 26 is established after a short time. At this stage, the current consumption of the pump drive 14 is measured by the measuring device 34, and the temperature measured by the temperature sensor 36 is simultaneously monitored.

[0019] In Fig. Figure 2 shows curve 40, which represents the current consumption I of the pump drive 14 as a function of the temperature T of the hydraulic fluid. Since the hydraulic system must function at ambient temperatures between -40 °C and +60 °C, the defined range of curve 40 is the temperature range from -40 °C to +100 °C. Because the viscosity of the hydraulic fluid increases with decreasing temperature, the current consumption rises significantly at lower temperatures.

[0020] Curve 42 in Fig. Figure 2 shows the current draw I as a function of temperature T for the case where the filter 26 is partially loaded with particles from the hydraulic fluid. It can be seen that the current draw is higher at all temperatures than at a comparable temperature when the filter is new. At the current temperature T of the hydraulic fluid, the current draw is measured using the measuring device 34, and the difference ΔI to curve 40 (new curve) is compared with a threshold value. This threshold value can be temperature-dependent to account for the fact that the difference between curves 40 and 42 does not have to be constant over the entire temperature range.

[0021] In Fig.Figure 3 illustrates the essential steps of a measurement process used to check the filter condition. In step S1, the switching valve 30 is opened, and after a certain waiting period, the motor 14 is switched on. In step S2, it is checked whether the speed of the pump drive has reached a stable value. Optionally, the control unit 38 can have an additional input for the motor speed. However, it is also possible to simply implement step S2 by waiting until the speed has reliably stabilized.

[0022] If the condition checked in step S2 is met, the temperature T and the current consumption I are queried in step S3. Then, in step S4, it is checked whether the difference ΔI between the measured current consumption and the value of the new curve stored for the measured temperature is greater than a temperature-dependent threshold value R(T). If this is the case (J), it means that filter 26 needs to be replaced, and this is indicated by a warning signal in step S5. If ΔI is below the threshold value, the measurement process is terminated in step S6. Optionally, the switching valve 30 can be automatically closed at this point, allowing pressure to build up in the pressure accumulator 22. Alternatively, the relative load could be calculated to provide a prediction of the remaining service life.

[0023] Optionally, the measured pairs of values ​​for temperature T and current consumption I can be stored in control unit 38 over a longer period. If the hydraulic system is operated at different ambient temperatures, this results in a number of measurement points over time, which indicate the course of curve 42. These measurement results can be read out from time to time to determine whether a filter replacement is necessary. QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2016 215 909 A1

[0004] DE 10 2022 200 673 B3

[0004]

Claims

[1] Device for filter condition detection in a mobile hydraulic system, which has a tank (18) for holding hydraulic fluid, a temperature sensor (36) for measuring the temperature of the hydraulic fluid, a filter (26), a pump (16) driven by an electric motor (14) for conveying the hydraulic fluid from the tank (18) through the filter (26) to a consumer (10), and a lockable return path (28) connecting the outlet of the filter (26) to the tank (18), characterized by a controller (32) for controlling the speed of the motor (14), a measuring device (34) for measuring the current consumption (I) of the motor (14), and a control device (38) for evaluating pairs of values ​​of the temperature (T) and the current consumption (I). [2] Device according to claim 1, wherein the motor (14) is a brushless motor. [3] Device according to claim 2, wherein the controller (32) and / or measuring device (34) is integrated into the pump drive (14). [4] Device according to one of the preceding claims, in which the return path (28) contains a switching valve (30) whose state can be detected and / or controlled by the control unit (38).

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