US20230003213A1

US20230003213A1 - Double-flow pump unit, and method for controlling same

Info

Publication number: US20230003213A1
Application number: US17/779,742
Authority: US
Inventors: Yunfan Wei; Marco Grethel; Carsten Mayer
Original assignee: Schaeffler Technologies AG and Co KG
Current assignee: Schaeffler Technologies AG and Co KG
Priority date: 2019-12-03
Filing date: 2020-11-06
Publication date: 2023-01-05
Also published as: DE102019132770B3; CN115151730A; WO2021110202A1

Abstract

A pump unit includes an electric motor and a pump with a duct. The pump is rotationally driven by the electric motor to provide a setpoint volumetric flow to the duct. A rotational speed controller is configured to, during operation of the pump, determine a setpoint rotational speed based on a fixed-point iteration of an initial rotational speed. The setpoint rotational speed is associated with a setpoint volumetric flow. The rotational speed controller is further configured to operate the pump at the setpoint rotational speed.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

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.

TECHNICAL FIELD

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.

BACKGROUND

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.

SUMMARY

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 n_setresults from equation (1)
n _set =Q _Soll/(V _d*η_V) (1)
where Q_Sollis the setpoint volumetric flow and V_dis displacement volume of the pump and the η_Vis 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 η_Vcan, 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.

BRIEF DESCRIPTION OF THE DRAWINGS

The disclosure is explained in more detail with reference to the exemplary embodiments shown in FIGS. 1 to 6 . In the figures:

FIG. 1 shows a schematic hydraulic plan for a single-flow pump unit,

FIG. 2 shows a method for operating the pump unit of FIG. 1 using a fixed-point iteration,

FIG. 3 shows a schematic hydraulic plan for a double-flow pump unit,

FIG. 4 shows a method for operating the pump unit of FIG. 3 using a fixed-point iteration,

FIG. 5 shows a schematic hydraulic plan for a double-flow pump unit with a hydraulic coupling of the ducts,

FIG. 6 shows a method for operating the pump unit of FIG. 5 using a fixed-point iteration.

DETAILED DESCRIPTION

FIG. 1 shows a schematically simplified representation of a pump unit 100 with a single-flow pump 105, which is rotationally driven by an electric motor 110, which sucks in hydraulic fluid from a sump 115 and feeds a setpoint volumetric flow Q_Sollinto a duct 120; for example, for actuating a hydraulically operated clutch, parking lock or brake.
The setpoint volumetric flow Q_Sollis adjusted by a rotational speed controller 125 from a setpoint rotational speed n_setand a current actual rotational speed n_actof the pump 105.
The setpoint rotational speed n_setof the pump 105 of FIG. 1 is determined using a routine 130 shown in FIG. 2 . In block 135, the pump 105 is operated at an initial rotational speed n_I, which is formed from the quotient of the desired setpoint volumetric flow Q_Solland a displacement volume V_dof the pump 105. In a fixed-point iteration 140, when the pump 105 is running, in a run of one or more iteration steps, the current speed n_actof the pump 105 is assigned, for example by interpolation, from a table in block 145 with the characteristic diagram of speed-dependent efficiencies η_Vand, if necessary, other variables such as a temperature of the hydraulic fluid and the like. The setpoint rotational speed n_setis then determined in block 150 from the quotient of the setpoint volumetric flow Q_Solland the displacement volume V_dcorrected with the efficiency η_V. In order to carry out further iteration steps 155, if necessary, a branch is made to block 145. 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 140, a safety value can be applied to the setpoint rotational speed n_setin block 160, as shown here, multiplied by a safety factor F greater than one.
FIG. 3 shows a schematically simplified representation of the pump unit 200 with a double-flow pump 205, which is rotationally driven by the electric motor 210, which sucks in hydraulic fluid from the sump 215 and feeds setpoint volumetric flows Q_Cool, Q_Sysinto two ducts, namely a low-pressure duct 220 and a high-pressure duct 221; for example, to cool or lubricate hydraulic components and to actuate a hydraulically actuated clutch, brake or parking lock.
The setpoint volumetric flows Q_Cool, Q_Sysare adjusted by means of the rotational speed controller 225 from the setpoint rotational speed n_setand the current actual rotational speed n_actof the pump 205. The ratio of the setpoint volumetric flows Q_Cool, Q_Systo 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 n_setof pump unit 100 in FIG. 1 , the determination of the setpoint rotational speeds n_set,LP, n_set,HPfor setting the setpoint volumetric flows Q_Cool, Q_Sysof the pump 205 of FIG. 3 is carried out separately from one another in the routine 230 shown in FIG. 4 .
In block 237, the pump 205 is operated at the initial rotational speed n_Irotational speed, which corresponds to the initial rotational speeds n_I,LP, n_I,HPof blocks 235, 236, which is formed from the quotients of the desired setpoint volumetric flows Q_Cool, Q_Sysand the displacement volume V_d,LP, V_d,HPof 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 n_actof the pump 205 is assigned, for example by interpolation, from the respective blocks 245, 246 with characteristic diagrams of the speed-dependent efficiencies η_V,LP, η_V,HPand, if necessary, other variables such as the temperature of the hydraulic fluid and the like. The setpoint rotational speeds n_set,LP, n_set,HPare then determined in blocks 250, 251 from the quotients of the setpoint volumetric flows Q_Cool, Q_Sysand the displacement volume V_d,HP, V_d,LPcorrected with the efficiencies η_V,LP, η_V,HP.
For the robust and safe implementation of both the lubrication/cooling of components using the setpoint volumetric flow Q_Cooland the actuation of components using the setpoint volumetric flow Q_Sys, the setpoint rotational speeds n_set,LP, n_set,HPof blocks 250, 251 are compared with one another in block 265 and a setpoint rotational speed n_set,Basisis determined from the highest of the two setpoint rotational speeds n_set,LP, n_set,Hp. This setpoint rotational speed n_set,Basisis 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 n_set,Basisin block 260, as shown here, multiplied by the safety factor F greater than one.
FIG. 5 shows the pump unit 300, which is similar to the pump unit 200 in FIG. 3 , in a schematically simplified representation with the double-flow pump 305, which is rotationally driven by the electric motor 310, which sucks in hydraulic fluid from the sump 315 and feeds the setpoint volumetric flows Q_Cool, Q_Sysinto the two ducts, namely the low-pressure duct 320 and the high-pressure duct 321; for example, to cool or lubricate hydraulic components and to actuate a hydraulically actuated clutch, brake or parking lock.
The setpoint volumetric flows Q_Cool, Q_Sysare adjusted by means of the rotational speed controller 325 from the setpoint rotational speed n_setand the current actual rotational speed n_actof the pump 305. The ratio of the setpoint volumetric flows Q_Cool, Q_Systo 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 Q_Cooland Q_Sysare 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 Q_Coolcan increase if required.
The routine 330 shown in FIG. 6 shows the control of the setpoint volumetric flows Q_Cool, Q_Sysfor the pump unit 300 of FIG. 5 based on the setpoint rotational speed n_set,Basis. Here, the routine 330 corresponds to the routine 230 of FIG. 4 up to the determination of the setpoint rotational speed n_set,Basisin block 265. The setpoint rotational speed n_set,Basisdetermined in block 365 of the routine 330 or in another determination method is adapted to the influence of hydraulic coupling 370 in the additional fixed-point iteration 380. Reference is made to the procedure of routine 230 of FIG. 4 for determining the setpoint rotational speed n_set,Basis.
The influence of the hydraulic coupling 370 is corrected in that the efficiencies η_v,HP, η_v,LPare again determined from blocks 345, 346; for example, by means of interpolation, based on the previously determined setpoint rotational speed n_set,Basis. In block 385, the corrected setpoint rotational speed n_set,erwis determined from the setpoint rotational speed n_set,Basis, taking into account the determined efficiencies η_v,HP, η_v,LP. The corrected setpoint rotational speed n_set,erwresults from the quotient of the numerator with the setpoint volumetric flow Q_Sysof the high-pressure duct 321 plus the product of the efficiency η_v,LPof the pump flow for the low-pressure duct 320, the displacement volume V_d,LPof the pump flow for the low-pressure duct 320 and the current setpoint rotational speed n_set,Basisand the denominator with the sum of the products of the efficiencies η_v,HP, η_v,LPeach multiplied by the displacement volumes V_d,HP, V_d,LPof 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 n_set,erwat 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 n_set,erwin 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.

LIST OF REFERENCE SYMBOLS

100 Pump unit
105 Pump
110 Electric motor
115 Sump
120 Duct
125 Rotational speed controller
130 Routine
135 Block
140 Fixed-point iteration
145 Block
150 Block
155 Iteration step
160 Block
200 Pump unit
205 Pump
210 Electric motor
215 Sump
220 Low-pressure duct
221 High-pressure duct
225 Rotational speed controller
230 Routine
235 Block
236 Block
237 Block
240 Fixed-point iteration
245 Block
246 Block
250 Block
251 Block
255 Iteration step
260 Block
265 Block
300 Pump unit
305 Pump
310 Electric motor
315 Sump
320 Low-pressure duct
321 High-pressure duct
325 Rotational speed controller
330 Routine
345 Block
346 Block
360 Block
365 Block
370 Hydraulic coupling
375 Pressure-limiting valve
380 Fixed-point iteration
385 Block
390 Iteration step
F Safety factor
n_actCurrent actual rotational speed
n_IInitial rotational speed
n,^IHPInitial rotational speed
n_I,LPInitial rotational speed
n_set,HPSetpoint rotational speed
n_set,LPSetpoint rotational speed
n_setSetpoint rotational speed
n_set,BasisSetpoint rotational speed
n_set,erwSetpoint rotational speed
Q_CoolSetpoint volumetric flow
Q_SollSetpoint volumetric flow
Q_SysSetpoint volumetric flow
V_dDisplacement volume
V_d,HPDisplacement volume
V_d,LPDisplacement volume
η_VEfficiency
η_V,HPEfficiency
η_V,LPEfficiency

Claims

1. A pump unit, comprising:

an electric motor;

a pump having a duct and being rotationally driven by the electric motor to provide a setpoint volumetric flow to the duct, and

a rotational speed controller configured to:

during operation of the pump, determine a setpoint rotational speed of the pump based on a fixed-point iteration of an initial rotational speed of the pump, wherein the setpoint rotational speed is associated with a setpoint volumetric flow; and

operate the pump at the setpoint rotational speed.

2. The pump unit according to claim 1, wherein the pump includes a second duct, the pump being rotationally driven by the electric motor to provide a second setpoint volumetric flow to the second duct.

3. The pump unit according to claim 2, wherein the duct and the second duct are hydraulically coupled to one another via a pressure-limiting valve.

4. The pump unit according to claim 2, wherein the duct is a high-pressure duct configured to actuate a component, and the second duct is a low-pressure duct configured to provide a fluid supply to the component, and wherein the component is a clutch, a parking lock, or a disk set of a variator of a continuously variable belt transmission.

5. A method for controlling a pump unit, comprising:

determining an initial rotational speed of the pump based on an efficiency of the pump and a required setpoint volumetric flow, wherein the efficiency is a maximum efficiency for the pump or is equal to one;

determining a setpoint rotational speed based on a specified number of iteration steps of the initial rotational speed and a correction value from the efficiency of the pump, wherein the correction value is determined based on the initial speed and the setpoint volumetric flow, wherein the setpoint rotational speed is associated with a setpoint volumetric flow; and

operating the pump at the setpoint rotational speed.

6. The method according to claim 5, wherein the specified number of iteration steps is odd.

7. The method according to claim 5, further comprising applying a safety value to the setpoint rotational speed.

8. The method according to claim 5, wherein the pump unit includes two ducts separate from each other, the method further comprising:

determining the initial rotational speed of the pump for each duct based on the efficiency of the pump for respective duct and the required setpoint volumetric flow for each duct;

determining the setpoint rotational speed of the pump for each duct based on the specified number of iteration steps of the initial rotational speed for the respective duct and the correction value of the efficiency for the respective duct; and

operating the pump at a maximum of the determined setpoint rotational speeds.

9. The method according to claim 5, wherein the pump includes two ducts connected to each other via a hydraulic coupling, the method further comprising:

determining the setpoint rotational speed of the pump for each duct based on the specified number of iteration steps of the initial rotational speed for the respective duct and the correction value of the efficiency for the respective duct;

determining a corrected setpoint rotational seed based on a maximum of the determined setpoint rotational speeds, and a volume exchange via the hydraulic coupling; and

operating the pump at the corrected setpoint rotational speed.

10. The method according to claim 9, wherein a size of the volume exchange is determined from the efficiencies of the pump for the ducts at the maximum of the determined setpoint rotational speeds.

11. The pump unit according to claim 2, wherein the rotational speed controller is further configured to determine a second setpoint rotational speed based on a fixed-point iteration of a second initial rotational speed of the pump, the second setpoint rotational speed being associated with the second setpoint volumetric flow.

12. The pump unit according to claim 11, wherein the rotational speed controller is further configured to operate the pump at a maximum of the setpoint rotational speed and the second setpoint rotational speed.

13. The pump unit according to claim 11, wherein the rotational speed controller is further configured to selectively operate the pump at one of the setpoint rotational speed or the second setpoint rotational speed.

14. The pump unit according to claim 11, wherein the rotational speed controller is further configured to determine the second initial rotational speed based on a desired setpoint volumetric flow through the second duct and a displacement volume of the pump through the second duct.

15. The pump unit according to claim 14, wherein the rotational speed controller is further configured to determine the second setpoint rotational speed further based on an efficiency of the pump operating via the second duct.

16. The pump unit according to claim 11, wherein the rotational speed controller is further configured to determine the initial rotational speed based on a desired setpoint volumetric flow through the duct and a displacement volume of the pump through the duct.

17. The pump unit according to claim 16, wherein the rotational speed controller is further configured to determine the setpoint rotational speed further based on an efficiency of the pump operating via the duct.

18. The pump unit according to claim 1, wherein the rotational speed controller is further configured to determine the initial rotational speed based on a desired setpoint volumetric flow and a displacement volume of the pump.

19. The pump unit according to claim 18, wherein the rotational speed controller is further configured to determine the setpoint rotational speed further based on an efficiency of the pump.

20. The pump unit according to claim 3, wherein the rotational speed controller is further configured to:

determine a volume exchange via the hydraulic coupling based on an efficiency, at the maximum setpoint rotational speed, of the pump for each duct;

determine a corrected setpoint rotational speed based on the volume exchange and the maximum setpoint rotational speed; and

operate the pump at the corrected setpoint rotational speed.