METHOD FOR REGULATING A VOLUME FLOW RATE AND TEST STAND FOR SIMULATING A LIQUID CIRCUIT

Abstract

A method for regulating a volume flow rate, and a test stand with a liquid circuit for carrying out the method is provided. A pump and a flow control valve are connected in series in the liquid circuit, and the orifice width of the flow control valve is set as a function of a setpoint value of the volume flow rate of the liquid, in order to specify, on the basis of the orifice width, a characteristic curve of the pump that plots the volume flow rate over the differential pressure. Once a characteristic curve has been specified, the differential pressure of the pump is set such that the volume flow rate corresponds to the setpoint value of the volume flow rate.

Claims

1. A method for regulating a volume flow rate of a first liquid circuit having a liquid, the method comprising: connecting a pump and a flow control valve in series in the first liquid circuit; setting an orifice width of the flow control valve as a function of a setpoint value of the volume flow rate of the liquid such that a first derivative of a characteristic curve, which plots the volume flow rate over a differential pressure of the pump, has a value that, at the setpoint value of the volume flow rate, is favorable for regulating the volume flow rate by setting the differential pressure; and setting the differential pressure of the pump such that the volume flow rate substantially corresponds to the setpoint value of the volume flow rate.

2. The method according to claim 1, wherein the orifice width is set such that the differential pressure does not exceed a predefined critical value, and wherein the critical value is no higher than 1.0 bar, 0.5 bar, or 0.3 bar.

3. The method according to claim 1, wherein the orifice width is chosen from a predefined selection of orifice widths.

4. The method according to claim 1, wherein the temperature of the liquid is regulated by at least one Peltier element.

5. The method according to claim 4, wherein the setpoint value of the volume flow rate and a setpoint value for the temperature are computed by a processor based on a software model.

6. The method according to claim 5, wherein the processor is built into a simulator or a hardware-in-the-loop simulator, wherein the simulator or the hardware-in-the-loop simulator controls the flow control valve, the pump, and the at least one Peltier element, and wherein a temperature of a unit under test is influenced by the first liquid circuit.

7. A test stand for simulating a liquid circuit for temperature regulation, the test stand comprising: a first liquid circuit with a liquid; a pump; and a flow control valve, the pump and the flow control valve being connected in series in the first liquid circuit, wherein the test stand is configured to read in a setpoint value of a volume flow rate of the liquid and set an orifice width of the flow control valve as a function of the setpoint value of the volume flow rate such that a first derivative of a characteristic curve, which plots the volume flow rate over a differential pressure of the pump, has a value that, at the setpoint value of the volume flow rate, is favorable for regulating the volume flow rate by setting the differential pressure, and wherein the test stand adjusts the differential pressure of the pump such that the volume flow rate substantially corresponds to the setpoint value of the volume flow rate.

8. The test stand according to claim 7, wherein the test stand reads in a setpoint value of the temperature of the liquid, and regulates a temperature of the liquid by at least one Peltier element.

9. The test stand according to claim 8, wherein a storage tank for the liquid is incorporated in the first liquid circuit and in a second liquid circuit, and wherein the at least one Peltier element is located on the second liquid circuit.

10. The test stand according to claim 7, wherein a processor for processing a software model is built into the test stand, wherein the test stand determines the setpoint values for the volume flow rate and the temperature via a software model.

11. The test stand according to claim 7, wherein the test stand is configured to accommodate a unit under test and to influence the temperature of the unit under test by the first liquid circuit.

12. The test stand according to claim 11, wherein the test stand has two separate components, wherein a processor is built into a first component, wherein the unit under test is built into the first component or the first component is configured to accommodate the unit under test, wherein the pump and the flow control valve are built into the second component, and wherein the first liquid circuit is routed between the first component and the second component.

13. The test stand according to claim 7, wherein the test stand is configured to select an orifice width from a predefined selection of orifice widths as a function of the setpoint value of the volume flow rate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The present invention will become more fully understood from the detailed description given hereinbelow and the accompanying drawings which are given by way of illustration only, and thus, are not limitive of the present invention, and wherein:

[0023] FIG. 1 is a representation of a test stand according to an embodiment of the invention;

[0024] FIG. 2 is a schematic representation of the hydraulics built into the test stand for influencing the temperature of the unit under test; and

[0025] FIG. 3 is a drawing of the characteristic curves of the pump as a function of the orifice width of the flow control valve.

DETAILED DESCRIPTION

[0026] The illustration in FIG. 1 shows a perspective representation of a test stand HIL designed as a hardware-in-the-loop simulator with a unit under test UUT. In the application example shown, the unit under test UUT is an intelligent DC-to-DC converter for a battery cell of a hybrid vehicle. The intelligent DC-to-DC converter has an integrated electronic control unit with a dedicated processor, which is to say that the actual DC-to-DC converter and the control unit for controlling the DC-to-DC converter are designed as an inseparable unit. The intelligent DC-to-DC converter is also equipped with a water passage, and is designed to be built into a water circuit for cooling the intelligent DC-to-DC converter.

[0027] The test stand HIL is constructed of two separate components. The processor unit CPU with the processor of the test stand HIL and the unit under test UUT are built into a first component CMP1. Also built into the first component are: a power supply unit PSU, a plug-in chassis RCK for a multiplicity of plug-in circuit boards, in particular I/O cards and cards for supporting and reducing the load on the processor CPU, and an electrical system for simulating the electrical environment of the unit under test UUT in the production vehicle in physical form. In particular, the electrical system has: a high-voltage power supply HVPS as the voltage source for the high-voltage side of the DC-to-DC converter UUT, a high-voltage load as an energy sink for the high-voltage side of the DC-to-DC converter UUT, a low-voltage power supply LVPS as the voltage source for the low-voltage side of the DC-to-DC converter UUT, and a low-voltage load LVPD as an energy sink for the low-voltage side of the DC-to-DC converter UUT.

[0028] The processor unit CPU of the test stand HIL is programmed with a software model to simulate an environment of the unit under test in hard real time, to provide input data to the unit under test on the basis of the software model, and to take into account output data from the unit under test during processing of the software model.

[0029] Hydraulics are built into a second component CMP2 in order to reproduce in physical form the water cooling of the unit under test simulated by the software model. A first liquid circuit CCL1, filled with liquid water, is routed between the first component CMP1 and the second component CMP2. The unit under test UUT is incorporated by means of its water passage into the first liquid circuit CCL1, so that the temperature of the unit under test UUT is influenced by means of the first liquid circuit CCL1.

[0030] An I/O card 10 is inserted in the plug-in chassis RCK, and the first component CMP1 is designed to exchange data between the processor unit CPU and a peripheral device of the first component CMP1 via the I/O card 10. A data link DL is established between the I/O card 10 and the second component CMP2 by means of data cables, and the test stand HIL is configured to use the data link DL to transmit control signals for actuators to the second component CMP2 and to transmit sensor values from the second component CMP2 to the processor unit CPU.

[0031] In a schematic representation, the illustration in FIG. 2 shows the hydraulics of the test stand HIL with the first liquid circuit CCL1 and a second liquid circuit CCL2. With the exception of one portion of the piping or hose lines of the first liquid circuit CCL1, the entire hydraulic system, in particular all components located spatially above the bracket labeled CMP2 in the illustration, is built into the second component CMP2. A storage tank TNK for the water is incorporated in the first liquid circuit CCL1 as well as in the second liquid circuit CCL2, and contains the great majority of the water in the hydraulic system. A first temperature sensor TS1, which is read by the processor unit CPU, measures the temperature of the water in the storage tank TNK. A float switch FLT measures the water level in the storage tank TNK, and is configured to turn off the test stand HIL if the water level drops.

[0032] The first liquid circuit CCL1 is routed between the first component CMP1 and the second component CMP2, and runs through the water passage of the unit under test UUT. A first pump P1 controlled by the first component CMP1 and a flow control valve VLV controlled by the first component CMP1 are connected in series in the first liquid circuit CCL1. The first pump P1 is located ahead of the flow control valve VLV with respect to the flow direction of the water in the first liquid circuit CCL1. A volume flow rate sensor VS, a second temperature sensor TS2, and a third temperature sensor TS3 are arranged on the first liquid circuit CCL1, and are read by the processor unit CPU. The volume flow rate sensor VS measures the volume flow rate in the first liquid circuit. The second temperature sensor TS2 measures the water temperature ahead of the unit under test UUT, and the third temperature sensor TS3 measures the water temperature after the unit under test UUT. The processor unit CPU is configured to compute the energy balance, in particular the waste heat, of the unit under test UUT by means of the second temperature sensor TS2 and the third temperature sensor TS3.

[0033] On the basis of the software model, the processor unit computes a setpoint value for the volume flow rate in the first liquid circuit CCL1, and controls the flow control valve VLV as a function of the setpoint value of the volume flow rate so as to set a characteristic curve of the first pump P1. The processor unit CPU is configured to control the pump output of the first pump P1 so as to set the volume flow rate in the first liquid circuit such that the volume flow rate read in by the volume flow rate sensor VS corresponds to the setpoint value of the volume flow rate. The setpoint value of the volume flow rate computed by the software model is not a constant, but rather a variable quantity, and the processor unit CPU is configured to dynamically match the volume flow rate in the first liquid circuit CCL1 to the variable setpoint value of the volume flow rate.

[0034] The processor unit CPU is additionally configured to compute a setpoint value for the temperature of the water in the first liquid circuit CCL1 by means of the software model, and the second liquid circuit CCL2 is configured to regulate the temperature of the water in the storage tank TNK. A second pump P2 is arranged in the second liquid circuit CCL2, and is not controlled by the processor unit CPU, but instead operates with a constant pumping power. A number of Peltier elements PLT, represented in the drawing by a single Peltier element, are arranged on the second liquid circuit CCL2 in order to heat or cool the water in the second liquid circuit CCL2 as needed. The processor unit CPU is configured to read the water temperature in the first liquid circuit by means of the first temperature sensor TS1 and the second temperature sensor TS2, and to dynamically match the variable setpoint value for the temperature computed by means of the software model by controlling the Peltier elements PLT.

[0035] The Peltier elements PLT are coupled to the second liquid circuit CCL2 by means of a heat exchanger plate. In order to facilitate cooling of the water to below room temperature, the heat exchanger plate and the Peltier elements PLT are arranged to be suspended, and in particular are not attached to the housing wall of the second component CMP2. The waste heat of the Peltier elements PLT is removed from the second component CMP2 by fans.

[0036] Using a characteristic curve diagram of the first pump, the illustration in FIG. 3 shows the generation of a predefined selection of orifice widths of the flow control valve VLV. The characteristic curves shown in the diagram are examples and do not represent genuine characteristic curves or measurements that were actually carried out. The illustration serves merely to provide direction to the person skilled in the art for generating a predefined selection of orifice widths. To reproduce the disclosed exemplary embodiment of the test stand according to the invention, it is necessary to ascertain suitable characteristic curves of the first pump or to determine them by measurement.

[0037] The characteristic curve diagram shows three characteristic curves of the first pump P1 as a plot of the volume flow rate in the first liquid circuit CCL1, measured in liters per minute, over the differential pressure of the first pump P1, measured in bar, for three different cross-sectional areas A.sub.1, . . . , A.sub.3 of the flow in the flow control valve VLV. By way of example, three different cross-sectional areas or orifice widths of the flow control valve VLV are provided, depending on the current setpoint value of the volume flow rate: a first cross-sectional area A.sub.1 for heavy volume flow rates in the range from 4 to 6 L/min, a second cross-sectional area A.sub.2 for volume flow rates in the range from 2 to 4 L/min, and a third cross-sectional area A.sub.3 for light volume flow rates in the range from 1 to 2 L/min. The cross-sectional areas are chosen such that the applicable characteristic curve is neither too flat nor too steep within the volume flow rate interval assigned to the applicable cross-sectional area, i.e. the first derivative of the characteristic curve has a moderate value within the entire interval, and such that the differential pressure corresponding to the applicable setpoint value of the volume flow rate never exceeds a value of 0.3 bar.

[0038] It is a matter of course that an essentially arbitrary number of predefined orifice widths can be defined, depending on the requirements and exact construction of a specific test stand. The predefined selection of orifice widths is stored in the form of a digital table that assigns the predefined orifice widths to their applicable volume flow rate intervals, in a memory that can be read by the processor unit CPU. In order to match the volume flow rate to the applicable current setpoint value of the volume flow rate, the processor unit is configured to read out the flow control valve orifice width assigned to the current setpoint value of the volume flow rate, to set the flow control valve accordingly, and then to match the volume flow rate to the setpoint value of the volume flow rate by controlling the first pump.

[0039] A test stand constructed by the applicant based on the disclosed exemplary embodiment has 16 Peltier elements with a rating of 56 W each. The said test stand is capable of regulating the volume flow rate in a range from 1 L/min to 6 L/min and the temperature in a range from 10° C. to 80° C. with sufficient accuracy for the requirements of a hardware-in-the-loop simulation while never exceeding a differential pressure of 0.3 bar. The investigations that preceded the design have demonstrated that it is not possible to achieve regulation meeting these requirements using pump systems available on the market without additional measures, e.g., the use according to the invention of a flow control valve.

[0040] The invention being thus described, it will be obvious that the same may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are to be included within the scope of the following claims.