Patent Application
20230003213
The disclosure relates to a pump unit and to a method for controlling same, in particular for actuating and/or providing a supply to at least one component of a drive train of a motor vehicle by means of at least one setpoint volumetric flow, wherein a pump with at least one duct for the at least one setpoint volumetric flow is rotationally driven by an electric motor, and a rotational speed controller is provided for setting the at least one setpoint volumetric flow by means of rotational speed control of the pump.
A double-flow pump unit is described in the publication DE 10 2011 100 845 A1, wherein a first pump primarily cools components of a drive train and a second pump actuates a double clutch. Both pumps can be connected to a pressure accumulator by means of a hydraulic valve. Both pumps are controlled by means of a rotational speed control of an electric motor that drives them, wherein one of the pumps is separably connected to the electric motor by means of a clutch.
It is desirable to provide a pump unit that is robust and controllable with a minimal computing effort and a method for controlling it.
The pump unit, according to one exemplary embodiment of the disclosure, in particular actuates and/or provides a supply to at least one component of a drive train of a motor vehicle. For example, a clutch, for example, a separating clutch between an internal combustion engine and an electric machine of a hybrid drive train, at least one friction clutch between an internal combustion engine and a transmission, a parking lock, one or both axially displaceable disks of a variator of a continuously variable belt transmission or the like can be actuated by means of the pump unit by means of a first pump flow that supplies a high-pressure duct. In addition, cooling of the clutch, the disk sets of the belt or the like and their lubrication can be provided; for example, by means of a second pump flow that supplies a low-pressure duct. By setting an appropriate speed for a given displacement volume and efficiency, the pump unit sets a volumetric flow at the appropriate duct—the high-pressure and/or low-pressure duct. The at least one single-flow or double-flow pump of the pump unit is rotationally driven by an electric motor. The electric motor is controlled to set a speed for providing the at least one volumetric flow by means of a control unit with a rotational speed controller that provides speed control of the electric motor and thus of the pump.
The setting of a specified volumetric flow such as the setpoint volumetric flow is based on the setpoint rotational speed depending on the displacement volume of the pump and its efficiency. In this case, an initial rotational speed is output by the rotational speed controller and the setpoint rotational speed is determined using a fixed-point iteration of this initial rotational speed during operation of the pump.
The pump unit can have a single-flow or a double-flow pump. In the case of a double-flow pump, the pump unit can have a first high-pressure duct for actuating a component and a second low-pressure duct for providing a supply to a component. According to one embodiment, the high-pressure duct and the low-pressure duct of a double-flow pump can be connected to one another by means of a pressure-limiting valve.
The proposed method is used to control the aforementioned pump unit with its specified characteristics. Here, with a system-related specified efficiency of the pump and a necessary setpoint volumetric flow to fulfill the task of the pump unit, an initial rotational speed of the pump is determined, for example estimated, and the electric motor is operated at this initial rotational speed. The setpoint rotational speed resulting from the displacement volume of the pump and its volumetric efficiency, which can be a function of a speed of the pump, a temperature of the pump fluid and the like, cannot be set directly for the setpoint volumetric flow required, i.e., to be set. To determine and set the setpoint rotational speed of the pump, a correction value is determined based on the set initial rotational speed and a predetermined number of iteration steps and the setpoint volumetric flow with a known displacement volume, with which the setpoint rotational speed is determined and set from the initial rotational speed. The setpoint rotational speed nset results from equation (1)
n
set
=Q
Soll/(Vd*ηV) (1)
where QSoll is the setpoint volumetric flow and Vd is displacement volume of the pump and the ηV is the volumetric efficiency. In this case, each iteration step results in reduced correction values, which improve the setpoint rotational speed as the number increases. The efficiency ηV can, for example, be read out and interpolated from loop tables stored in the control unit. Alternatively, the maximum efficiency known for the pump or an efficiency equal to one can be used as a good approximation.
Due to the rotational speed of the electric motor approaching the desired setpoint rotational speed with the number of iteration steps, with alternating over- and under-compensation of the correction values, for safety reasons, it may be advantageous to restrict the setpoint rotational speed to odd numbers, at least during the adjustment process during the fixed-point iteration, so that at the expense of an economical operation, a functionally reliable setpoint rotational speed is always determined and set. For most applications, for example, the fixed-point iteration can be limited to one with sufficient accuracy of the setpoint rotational speed, i.e., it is sufficient to determine only one iteration step with a single correction value and to correct the initial rotational speed with this correction value in order to obtain a sufficiently accurate setpoint rotational speed.
It can also be advantageous to apply a safety value to the setpoint rotational speed determined from the at least one iteration step. For example, a safety factor can be added to the setpoint rotational speed determined, or a safety sum can be added. The safety value can be constant or adapted to the operating situation; for example, operating age, temperature, setpoint rotational speed and/or the like.
In the case of a single-flow pump, it is sufficient if the setpoint rotational speed calculates the setpoint volumetric flow of the single duct. In the case of a double-flow pump with two ducts, in particular a high-pressure duct and a separate low-pressure duct, it is advantageous to determine the setpoint rotational speed for each one using the proposed fixed-point iteration and to operate the double-flow pump at the maximum setpoint rotational speed required for one of the two setpoint volumetric flows. Here, alternatively or additionally, the duct that is prioritized with regard to its function; for example, the high-pressure duct when a component is actuated, or the low-pressure duct in the case of a critical temperature or lubrication, can be preferred and its required setpoint rotational speed can be set.
In a double-flow pump with two ducts, namely a high-pressure duct and a low-pressure duct connected thereto by means of a hydraulic coupling, for example a pressure relief valve, a setpoint rotational speed can be determined for each duct after each iteration step. The maximum setpoint rotational speed required for one of the two setpoint volumetric flows can be determined from these two setpoint rotational speeds. The setpoint rotational speed for the current most important function can be prioritized. Subsequently or before the prioritization, the selected setpoint rotational speed can be corrected iteratively with a size of a volume exchange via the hydraulic coupling; for example, a volume loss via the pressure relief valve. This size of the volume exchange can be determined from the current efficiencies of the pump at the current speed of the low-pressure duct and the high-pressure duct.
The disclosure is explained in more detail with reference to the exemplary embodiments shown in
The setpoint volumetric flow QSoll is adjusted by a rotational speed controller 125 from a setpoint rotational speed nset and a current actual rotational speed nact of the pump 105.
The setpoint rotational speed nset of the pump 105 of
The setpoint volumetric flows QCool, QSys are adjusted by means of the rotational speed controller 225 from the setpoint rotational speed nset and the current actual rotational speed nact of the pump 205. The ratio of the setpoint volumetric flows QCool, QSys to one another is specified here by the displacement volumes and the efficiency of the double-flow pump 205. Advantageously, the displacement volumes for the two ducts are similar.
Corresponding to the determination of the setpoint rotational speed nset of pump unit 100 in
In block 237, the pump 205 is operated at the initial rotational speed nI rotational speed, which corresponds to the initial rotational speeds nI,LP, nI,HP of blocks 235, 236, which is formed from the quotients of the desired setpoint volumetric flows QCool, QSys and the displacement volume Vd,LP, Vd,HP of the pump 205. In the fixed-point iteration 240, when the pump 205 is running, in a run of one or more iteration steps 255, the current speed nact of the pump 205 is assigned, for example by interpolation, from the respective blocks 245, 246 with characteristic diagrams of the speed-dependent efficiencies ηV,LP, ηV,HP and, if necessary, other variables such as the temperature of the hydraulic fluid and the like. The setpoint rotational speeds nset,LP, nset,HP are then determined in blocks 250, 251 from the quotients of the setpoint volumetric flows QCool, QSys and the displacement volume Vd,HP, Vd,LP corrected with the efficiencies ηV,LP, ηV,HP.
For the robust and safe implementation of both the lubrication/cooling of components using the setpoint volumetric flow QCool and the actuation of components using the setpoint volumetric flow QSys, the setpoint rotational speeds nset,LP, nset,HP of blocks 250, 251 are compared with one another in block 265 and a setpoint rotational speed nset,Basis is determined from the highest of the two setpoint rotational speeds nset,LP, nset,Hp. This setpoint rotational speed nset,Basis is used to correct the pump 205.
To carry out further iteration steps 255, if necessary, a branch is made after block 265 to block 245. It has proven to be advantageous to carry out an odd number of iteration steps, in particular—as shown—only one iteration step.
At the end of the fixed-point iteration 240, a safety value can be applied to the setpoint rotational speed nset,Basis in block 260, as shown here, multiplied by the safety factor F greater than one.
The setpoint volumetric flows QCool, QSys are adjusted by means of the rotational speed controller 325 from the setpoint rotational speed nset and the current actual rotational speed nact of the pump 305. The ratio of the setpoint volumetric flows QCool, QSys to one another is specified here by the displacement volumes and the efficiency of the double-flow pump 305. Advantageously, the displacement volumes for the two ducts are similar.
In contrast to the pump unit 200, a hydraulic coupling 370 is provided in the pump unit 300 between the high-pressure duct 321 and the low-pressure duct 320, so that the setpoint volumetric flows QCool and QSys are designed to be dependent on one another. The hydraulic coupling 370 is formed by a pressure-limiting valve 375, which is controlled by the system pressure of the high-pressure duct 321 and diverts an overpressure that occurs in the high-pressure duct 321 into the low-pressure duct 320, so that its setpoint volumetric flow QCool can increase if required.
The routine 330 shown in
The influence of the hydraulic coupling 370 is corrected in that the efficiencies ηv,HP, ηv,LP are again determined from blocks 345, 346; for example, by means of interpolation, based on the previously determined setpoint rotational speed nset,Basis. In block 385, the corrected setpoint rotational speed nset,erw is determined from the setpoint rotational speed nset,Basis, taking into account the determined efficiencies ηv,HP, ηv,LP. The corrected setpoint rotational speed nset,erw results from the quotient of the numerator with the setpoint volumetric flow QSys of the high-pressure duct 321 plus the product of the efficiency ηv,LP of the pump flow for the low-pressure duct 320, the displacement volume Vd,LP of the pump flow for the low-pressure duct 320 and the current setpoint rotational speed nset,Basis and the denominator with the sum of the products of the efficiencies ηv,HP, ηv,LP each multiplied by the displacement volumes Vd,HP, Vd,LP of the pump ducts of the high-pressure duct 321 and the low-pressure duct 320.
If one or more iteration steps 390, in particular an odd number of iteration steps, are desired, a branch is made to the respective currently determined expanded setpoint rotational speed nset,erw at the start of the fixed-point iteration.
At the end of the fixed-point iteration 380, a safety value can be applied to the corrected setpoint rotational speed nset,erw in block 360, as shown here, multiplied by the safety factor F greater than one.
Based on the fixed-point iteration 380 shown, multi-dimensional tables that depict the hydraulic influence of the hydraulic coupling 370 and their complex algorithmic consideration can be dispensed with.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2019 132 770.9 | Dec 2019 | DE | national |
This application is the U.S. National Phase of PCT Appln. No. PCT/DE2020/100956 filed Nov. 6, 2020, which claims priority to DE 102019132770.9 filed Dec. 3, 2019, the entire disclosures of which are incorporated by reference herein.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/DE2020/100956 | 11/6/2020 | WO |
