METHOD FOR CONTROLLING A HYDRAULIC UNIT IN PARTICULAR FOR A DRIVETRAIN OF A MOTOR VEHICLE, HYDRAULIC UNIT AND DRIVETRAIN WITH HYDRAULIC UNIT

Abstract

A method for controlling a hydraulic unit with a rotational-speed-controlled pump which, at an outlet side, provides at least two fluid flows in a manner switched by means of switching valves actuating at least one slave cylinder and for providing a volume flow which is controlled based on a rotational speed of the pump. To set the volume flow, an efficiency of the pump is calculated base on a comparison of a known slave cylinder volume of the at least one slave cylinder and a quantity of fluid of the pump for the filling of the at least one slave cylinder.

Description

The invention relates to a method for controlling a hydraulic unit, a hydraulic unit and a drivetrain with a hydraulic unit comprising a rotational-speed-controlled pump, subject to leakage, which, at an outlet side, provides at least two fluid streams in a manner switched by means of switching valves, specifically for the purposes of actuating at least one slave cylinder and for a further volume flow which is controlled on the basis of a rotational speed of the pump.

Unpublished patent application No. 10 2019 102 249.5 describes a method for determining a leakage, a hydraulic unit for carrying out this method and a drivetrain comprising this hydraulic unit. The content of this application is the entire content of this patent application.

The object of the invention is the further development of a method, a hydraulic unit for carrying out a method for its control, and a drivetrain comprising this hydraulic unit. In particular, the object of the invention is that of controlling a volume flow of the hydraulic unit in an improved manner.

The object is achieved by the subject matter of claims 1, 9 and 10. The claims dependent on claim 1 represent advantageous embodiments of the subject matter of claim 1.

The proposed method is used for controlling a hydraulic unit, in particular for a drivetrain of a motor vehicle, with a rotational-speed-controlled pump that is subject to leakage. The pump can be designed, for example, as a non-pressure-compensated gear pump, in which the fluid is discharged as a pressure medium reducing the pressure via a leakage line into a fluid sump when the pressure is not reduced via the outlet. The pump provides at least two fluid streams on the outlet side. For example, a fluid flow can be provided dependent on a direction of rotation of the pump. The pump is preferably driven by an electric motor. The switching and provision of the fluid streams is achieved by means of switching valves, which are switched by a control device that preferably also controls the pump.

At least one fluid flow is used to actuate and pressurize at least one slave cylinder, substantially without fluid loss. At least two slave cylinders with two fluid flows switched by switching valves are preferably provided in a drivetrain, particular an entirely electrically operated drivetrain, wherein one slave cylinder actuates a separating clutch provided between a drive unit and a transmission and the other slave cylinder actuates a parking lock along a respectively specified actuation path. At least one further fluid flow is configured as a volume flow, which is set on the basis of a rotational speed of the pump and is used, for example, for cooling and/or lubricating components of the drivetrain, for example the separating clutch. Due to the system-related leakage of the pump, the leakage is determined by means of the proposed method. For this purpose, an efficiency of the pump is calculated on the basis of a comparison of a known slave cylinder volume of the at least one slave cylinder and a determined quantity of fluid of the pump for filling the at least one slave cylinder.

For example, the quantity of fluid is determined by integrating the fluid flow over a filling time of the slave cylinder volume. During filling of the at least one slave cylinder, all other fluid streams of the pump are preferably switched off or at least held constant. In order to hold the fluid flow constant over the filling time and thus to simplify an integration or summing of the fluid flow quantity delivered per unit time, the pump can be operated at constant rotational speed during the filling time. For example, the rotational-speed-dependent fluid flow is summed along the actuation path for the at least one slave cylinder over the filling time between two piston positions, for example between a position with an unactuated parking lock and a position with an actuated parking lock.

The slave cylinder volume can, for example, be calculated from a piston base area and a path interval traveled between the two piston positions. At least one of the piston positions can be adjustable over the operating time, wherein the corresponding currently adjusted piston position is used as the basis for determining the slave cylinder volume.

Using the efficiency determined, for example continuously or over the operating time of the pump, the fluid streams output from the pump can be determined independently of a leakage of the pump. In this case, a leakage which may be pressure-, temperature- or wear-related or caused in another way is detected by means of determining the efficiency, and the fluid streams are correspondingly corrected. The efficiency is thereby continuously adjusted to the current behavior of the pump. The volume flow for cooling and/or lubricating drivetrain components is preferably set according to the rotational speed of the pump and its efficiency. The efficiency is preferably determined by means of a parking lock actuating slave cylinder. It is possible in principle to determine the efficiency by means of a slave cylinder of the separating clutch. Due to the system-related use of the separating clutch, for example as a slipping separating clutch during ongoing driving operation, the slave cylinder of the parking lock is however preferred. For example, the efficiency of the pump can be adjusted at each actuation of the parking lock or at longer intervals.

The object is also achieved through a hydraulic unit with a pump, at least one slave cylinder, switching valves and a control unit such as a control device with an implemented routine for carrying out the proposed method.

The object is also achieved by a drivetrain for a motor vehicle comprising this drivetrain with a drive unit, in particular an entirely electrically operated drive unit, a transmission and a separating clutch arranged between the drive unit and the transmission, and a parking lock, wherein the separating clutch and the parking lock is actuated or actuatable by means of the proposed hydraulic unit.

The invention is explained in more detail with reference to the exemplary embodiment shown in FIGS. 1 to 4. In the figures:

FIG. 1 shows a schematic diagram of a hydraulic unit for carrying out the method according to the invention,

FIG. 2 shows a schematic diagram of a hybrid drive interacting with the hydraulic unit of FIG. 1,

FIG. 3 shows a flow diagram of the proposed method, and

FIG. 4 shows a diagram for determining the efficiency of the pump of FIG. 1.

FIG. 1 shows a schematic diagram of a hydraulic unit 1 for carrying out the method according to the invention. The hydraulic unit 1 contains the pump 2 which is equipped, for example, as a gear pump with a leakage, which is not shown, into the fluid sump 13, which is connected on one side to the coolant line 3 in order to provide a rotary-speed-regulated volume flow. The coolant line 3 feeds the fluid, for example a pressure medium such as oil, to the first consumer 4 designed, for example, as a heat exchanger. The fluid 7 is fed to this first consumer 4 for the purpose of cooling or lubrication. On the other side, the pump 2 is connected to the pressure line 5. The pressure line 5 is used to pressurize the slave cylinders 6, 8 of the parking lock 9 and the separating clutch 17. The switching valve 10, such as a two-way switching valve for example, is provided in order to selectively actuate the slave cylinders 6, 8.

The pump 2 is designed as an electrically driven reversible pump, in order to supply the fluid 7 to the coolant line 3 in a first direction of rotation, and to the pressure line 5 in a second direction of rotation. The pump 2 is driven by an electric motor 11 which is controlled by the control device 12. The pump 2, the electric motor 11 and the control device 12 form an electric pump actuator. A pressure sensor 14 is arranged in the pressure line 5, which is connected to the control device 12 of the pump 2 and, via this, to power electronics 15 that control the entire drive unit 1.

The switching valve 23, such as a two-way switching valve for example, is used for quickly opening the separating clutch 17 and for this purpose connects the slave cylinder 6 to the fluid sump 13.

In order to determine the efficiency of the pump 2 influenced by the leakage of the pump 2, the quantity of fluid output via the pressure line 5 when the switching valve 10 is switched to the slave cylinder 8 during an actuation of the slave cylinder 8 is detected as a delivered amount of the fluid and compared with the slave cylinder volume of the slave cylinder between the two positions A, B of the slave cylinder piston 21, for example forming their quotient. The efficiency determined in this way is used to correct the quantity of fluid for the volume flow of the coolant line 3 that is set depending on the rotational speed of the pump 2.

FIG. 2 shows a schematic diagram of the drivetrain 16 designed, for example, as a hybrid drivetrain. The drive unit 20 shown in front of the separating clutch 17 contains the internal combustion engine 24 and the electric machine 19. For an entirely electric design of the drivetrain 16, the internal combustion engine 24 can be omitted. The electric machine 18 and a transmission, not illustrated, connected upstream of the electric machine 18, for example an input transmission, are provided on the opposite side of the separating clutch 17. The parking lock 9 and the separating clutch 17 are actuated by the hydraulic unit 1 of FIG. 1. The two electric machines 18, 19 can be coupled or separated by means of the separating clutch 17 and can be designed for different rotational speeds of the drive 22. On the input side of the separating clutch 17, the internal combustion engine 24 is rigidly connected to the electric machine 19, which can work as a generator and, if necessary, during entirely electric driving, can provide electrical energy for the electric machine 18 by means of the electric machine 18. The electric machine 18 is directly coupled to the drive 22 of a motor vehicle comprising the drivetrain 16.

FIG. 3 shows the flow diagram 100 for carrying out the proposed method for determining the efficiency of the pump 2 with reference to the hydraulic unit 1 of FIG. 1. The method is started in block 103 and initialized in block 105. The parking lock 9 with its slave cylinder 8 is switched such that the pump 2 pressurizes the fluid 7 in order to disengage the parking lock 9, so that the slave cylinder piston 21 is moved from position A into position B and thereby travels a specified path interval. The slave cylinder volume is calculated from the known piston base area of the slave cylinder piston 21 and the path interval.

In branch 110, it is asked whether the parking lock 9 should be disengaged. If this is the case, in block 120, the pressure line 5 is switched to the slave cylinder 8 by means of the switching valve 10.

Then, in block 130, the rotational speed of the pump 2 is regulated at a specified value.

In branch 140, there is a wait until the specified value of the rotational speed has been adjusted. If this is the case, in block 150, the position A of the slave cylinder piston 21 is detected and stored. Then, in block 160, the quantity of fluid, which is dependent on the rotational speed of the pump 2, is detected.

In branch 170, it is checked whether a rotational speed has dropped below a target rotational speed. If this is not the case, the pump continues to operate at the specified rotational speed and integrates the quantity of fluid. If the rotational speed drops below the specified rotational speed, for example because the slave cylinder piston 21 strikes an end position or the actuation force is too high against the action of a spring element, then position B is fixed and the pump 2 switched off.

In block 190, the integrated quantity of fluid is determined and divided by the slave cylinder volume calculated from the path interval between the two positions A, B and the piston base area and the mechanical efficiency of the pump 2 is determined and stored.

FIG. 4 shows, with reference to the hydraulic unit 1 of FIG. 1, the diagram 200 with the two partial diagrams I, II over the filling time t of the slave cylinder 8. Partial diagram I shows the path of the slave cylinder piston 21 over time t and partial diagram II shows the rotational speed n of the pump 2 over time t.

Between positions A, B of the slave cylinder piston 21, the slave cylinder 8 is filled at constant rotational speed of the pump 2 and thus a linear rise of the slave cylinder piston 21. Therefore, a specified slave cylinder volume V is filled in the path interval Δs between positions A and B.

The pump 2 fills the slave cylinder 8 over the filling time t, wherein within the path interval Δs and therefore between the points in time t(A), t(B) of positions A, B, the quantity of fluid F is pumped by the pump 2 into the slave cylinder 8. Due to the leakage of the pump 2, the quantity of fluid F is smaller than the specified slave cylinder volume V and the ratio FN is the mechanical efficiency of the pump 2.

LIST OF REFERENCE SYMBOLS

• • 1 Hydraulic unit
  • 2 Pump
  • 3 Coolant line
  • 4 Consumer
  • 5 Pressure line
  • 6 Slave cylinder
  • 7 Fluid
  • 8 Slave cylinder
  • 9 Parking lock
  • 10 Switching valve
  • 11 Electric motor
  • 12 Control device
  • 13 Fluid sump
  • 14 Pressure sensor
  • 15 Power electronics
  • 16 Drivetrain
  • 17 Disconnect clutch
  • 18 Electric machine
  • 19 Electric machine
  • 20 Drive unit
  • 21 Slave cylinder piston
  • 22 Output drive
  • 23 Switching valve
  • 24 Internal combustion engine
  • 100 Flow diagram
  • 103 Block
  • 105 Block
  • 110 Branch
  • 120 Block
  • 130 Block
  • 140 Branch
  • 150 Block
  • 160 Block
  • 170 Branch
  • 180 Block
  • 190 Block
  • 200 Diagram
  • I Partial diagram
  • II Partial diagram
  • A Position
  • B Position
  • F Quantity of fluid
  • V Slave cylinder volume
  • n Rotational speed
  • s Actuation path
  • t Filling time
  • t(A) Point in time
  • t(B) Point in time
  • Δs Path interval

Claims

1. A method for controlling a hydraulic unit comprising: switching, via a switching valve, between at least two fluid flows at an outlet side of a rotational-speed-controlled pump, wherein one of the fluid flows actuates at least one slave cylinder and the other of the fluid flows provides a volume flow, which is controlled based on a rotational speed of the pump, andcalculating an efficiency of the pump based on a comparison of a known slave cylinder volume of the at least one slave cylinder and a quantity of fluid of the pump for the filling the at least one slave cylinder.

2. The method according to claim 1, further comprising determining the quantity of fluid by integrating the one fluid flow over a filling time of the slave cylinder volume.

3. The method according to claim 2, further comprising, during filling of the at least one slave cylinder, switching all other fluid flows of the pump off.

4. The method according to claim 2, further comprising operating the pump at a constant rotational speed during the filling time.

5. The method according to claim 2, further comprising integrating the one fluid flow along an actuation path for the at least one slave cylinder over the filling time between two positions of a slave cylinder piston.

6. The method according to claim 5, further comprising calculating the slave cylinder volume from a piston base area and a path interval traveled between the two positions.

7. The method according to claim 1, further comprising setting the volume flow according to the rotational speed and the efficiency of the pump.

8. The method according to claim 1, further comprising determining the efficiency by means of a parking lock actuating slave cylinder.

9. A hydraulic unit comprising a pump, at least one slave cylinder, a switching valve and a control device, wherein the control device is programmed to: switch, via a switching valve, between at least two fluid flows at an outlet side of the pump,determine a quantity of fluid of the pump for filling the at least one slave cylinder based on a fluid flow for actuating the slave cylinder; andcalculate an efficiency of the pump based on comparing a known slave cylinder volume of the at least one slave cylinder and quantity of fluid.

10. A drivetrain, comprising a drive unit, a transmission, a separating clutch arranged between the drive unit and the transmission, a parking lock, and a hydraulic unit including u pump, at least two slave cylinders, a switching valve, and a control device, wherein one slave cylinder is engaged with the separating clutch and another slave cylinder is engaged with the parking lock, wherein the control device is programmed to: selectively actuate the separating clutch or the parking lot via the switching valve;determine a quantity of fluid of the pump for filling the slave cylinder engaged with the actuated one of the parking lock or separating clutch based on a fluid flow for actuating the respective slave cylinder; andcalculate an efficiency of the pump based on comparing of a known slave cylinder volume of the respective slave cylinder and the quantity of fluid.

11. The hydraulic unit according to claim 9, wherein the control device is further programmed to determine the quantity of fluid by integrating the fluid flow over a filling time of the slave cylinder volume.

12. The hydraulic unit according to claim 11, wherein the control device is further programmed to integrate the fluid flow along an actuation path for the at least one slave cylinder over a filling time between two positions of a slave cylinder piston.

13. The hydraulic unit according to claim 11, wherein the control device is further programmed to, during filling of the at least one slave cylinder, stop all other fluid flows of the pump.

14. The hydraulic unit according to claim 11, wherein the control device is further programmed to operate the pump at a constant rotational speed during the filling time

15. The hydraulic unit according to claim 9, wherein the control device is further programmed to actuate the switching valve to provide the fluid flow for filling the at least one slave cylinder or a volume flow to a component, wherein the volume flow is based on a rotational speed of the pump.

16. The hydraulic unit according to claim 15, wherein the control device is further programmed to set the volume flow according to the rotational speed and the efficiency of the pump.