Method for controlling a hydraulic system

Abstract

A method for controlling a hydraulic system for actuating a drive train device of a drive train of a motor vehicle includes a first volumetric flow of a pressure medium being provided by an electrically operated pump, and a slave cylinder piston of a slave cylinder being actuated along an actuation path, in a manner controlled by a switch valve, via a second volumetric flow generated from the first volumetric flow. A leakage in the hydraulic system is determined from a comparison of the first and second volumetric flows.

Claims

1. A method for controlling a hydraulic system for actuating a drive train device of a drive train of a motor vehicle, comprising: providing a first volumetric flow of a pressure medium via an electrically operated pump; actuating, via a second volumetric flow generated from the first volumetric flow, a slave cylinder piston of a slave cylinder along an actuation path, in a manner controlled by a switch valve; during actuation of the slave cylinder, determining the first volumetric flow from rotational parameters and an electric current of an electric motor driving the pump, and mechanical constants of the hydraulic system; and determining a leakage in the hydraulic system from a comparison of the first and second volumetric flows.

2. The method according to claim 1, further comprising: determining, in an initial state, a first leakage; continuously comparing the first leakage with the leakage; and determining a measure of the leakage from the comparison.

3. The method according to claim 1, further comprising: neglecting a leakage of the slave cylinder and a leakage of the switch valve; and associating the leakage with the pump.

4. The method according to claim 1, wherein one of the mechanical constants is a mass moment of inertia of a rotor of the electric motor.

5. The method according to claim 1, wherein the mechanical constants include at least one of a compressibility constant, a damping of the pressure medium, and a displaced volume of the pump.

6. The method according to claim 1, further comprising, during actuation of the slave cylinder, determining the second volumetric flow from a piston surface area of the slave cylinder piston and an actuation speed of the slave cylinder piston.

7. The method according to claim 1, further comprising determining the leakage in a temperature-compensated manner.

8. The method according to claim 7, wherein a viscosity of the pressure medium is compensated.

9. The method according to claim 7, wherein a temperature-dependent damping of the pressure medium is compensated.

10. A method for controlling a hydraulic system for actuating a drive train device of a drive train of a motor vehicle, the method comprising: providing, via a pump, a first volumetric flow of a pressure medium to a switch valve; controlling the switch valve to provide a second volumetric flow of the pressure medium to actuate a piston of a cylinder, wherein the second volumetric flow is generated from the first volumetric flow; determining a pump leakage based on the first volumetric flow and the second volumetric flow; and detecting wear in the pump by comparing the determined leakage to an initial pump leakage determined in an initial state of the pump.

11. The method according to claim 10, further comprising, during actuation of the cylinder, determining the first volumetric flow based on rotational parameters and an electric current of an electric motor driving the pump, and mechanical constants of the hydraulic system.

12. The method according to claim 11, wherein one of the mechanical constants is a mass moment of inertia of a rotor of the electric motor.

13. The method according to claim 11, wherein the mechanical constants include at least one of a compressibility constant, a damping of the pressure medium, and a displaced volume of the pump.

14. The method according to claim 10, further comprising, during actuation of the cylinder, determining the second volumetric flow based on a piston surface area of the piston and an actuation speed of the piston.

15. The method according to claim 10, further comprising determining the pump leakage based additionally on neglecting a leakage of the switch valve and a leakage of the cylinder.

16. The method according to claim 10, further comprising determining the pump leakage in a temperature-compensated manner.

17. The method according to claim 16, wherein at least one of a viscosity of the pressure medium and a temperature-dependent damping of the pressure medium is compensated.

18. A method for controlling a hydraulic system for actuating a drive train device of a drive train of a motor vehicle, comprising: providing a first volumetric flow of a pressure medium via an electrically operated pump; actuating, via a second volumetric flow generated from the first volumetric flow, a slave cylinder piston of a slave cylinder along an actuation path, in a manner controlled by a switch valve; determining a leakage in the hydraulic system from a comparison of the first and second volumetric flows; determining, in an initial state, a first leakage; continuously comparing the first leakage with the leakage; and determining a measure of the leakage from the comparison.

19. The method according to claim 18, further comprising, during actuation of the cylinder, determining the first volumetric flow based on rotational parameters and an electric current of an electric motor driving the pump, and a mass moment of inertia of a rotor of the electric motor.

20. The method according to claim 18, further comprising, during actuation of the cylinder, determining the first volumetric flow based on rotational parameters and an electric current of an electric motor driving the pump, and mechanical constants of the hydraulic system, wherein the mechanical constants include at least one of a compressibility constant, a damping of the pressure medium, and a displaced volume of the pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The disclosure is explained in more detail with reference to the exemplary embodiment shown in FIGS. 1 to 3. In the figures:

(2) FIG. 1 shows a schematic representation of a hydraulic system for actuating two drive train devices,

(3) FIG. 2 shows a block diagram for determining the leakage of the hydraulic system of FIG. 1, and

(4) FIG. 3 shows a diagram with a simulation of an actuation of the slave cylinder of FIG. 1.

DETAILED DESCRIPTION

(5) With reference to the above equations (1) to (7), FIG. 1 shows the schematically illustrated hydraulic system 1 for actuating two drive train devices, which are not explicitly shown, and the determination of its leakage.

(6) The hydraulic system 1 contains the pump 3 driven by the electric motor 2, which sucks pressure medium 5 from the sump 4 and delivers it to the pressure line 6.

(7) The pressure line 6 leads to the switch valve 7, which alternatively connects to the slave cylinder 8 with the slave cylinder piston 9 displaceable along the actuation path x for actuating a parking lock (not shown) as one of the drive train devices in order to actuate it. Alternatively, the switch valve 7 connects the pressure line 6 to a slave cylinder (not shown) similar to the slave cylinder 8 along the arrow 10 for actuating a drive train device designed as a disconnect clutch of the drive train.

(8) The leakage of the hydraulic system 1 is limited to the determination of the leakage Q.sub.leakage of the pump 3, since the leakages of the switch valve 7 and the slave cylinder 8 are negligible. The leakage Q.sub.leakage is determined by comparing the first volumetric flow Q.sub.pump generated by the pump 3 and the second volumetric flow Q.sub.load for displacement of the slave cylinder piston 9 along the actuation path x.

(9) The electric motor 2 is designed as a brushless DC motor whose rotational parameters of a rotor, such as rotational angle ?, angular velocity {dot over (?)} and angular acceleration {umlaut over (?)}, are detected by means of an incremental angle sensor and evaluated by a control unit. Furthermore, the current i of the electric motor 2 for operating the pump 3 is detected and evaluated. The motor constant K.sub.e, the efficiency ? and the mass moment of inertia J of the rotor are known. From this, the first volumetric flow Q.sub.pump is determined at the calculated pressure p of the pressure medium 5 and its viscosity at a specified temperature. The second volumetric flow Q.sub.load is determined from the actuation speed {dot over (x)}, which is detected by a displacement sensor of the slave cylinder and evaluated by the control unit, and the known piston surface area A.sub.piston. From this, the leakage Q.sub.leakage is determined according to equation (7). A progression of the leakage Q.sub.leakage over the service life of the hydraulic system 1 can be monitored by comparison with a leakage detected at the start of operation and, if necessary, a state of wear of the pump 3 can be determined from this.

(10) With reference to equations (1) to (7) and FIG. 1, FIG. 2 shows the block diagram 11 for determining the leakage Q.sub.leakage or filtered leakage Q.sub.leakage,f from the actuation path x, the angular velocity {dot over (?)} of the electric motor 2 and the current i of the electric motor 2.

(11) The second volumetric flow Q.sub.load is calculated from the actuation path x by means of differentiation d/dt in block 12 and the piston surface area A.sub.piston in block 13.

(12) The angular velocity {dot over (?)} and the volume V.sub.d displaced by pump 2 in block 26 are used to calculate the first volumetric flow Q.sub.pump.

(13) In parallel to this, the angular velocity {dot over (?)}, the current i as input variables and the damping d in block 13, the displaced volume V.sub.d in block 14, the angular acceleration {umlaut over (?)} determined from the differentiation d/dt in block 15, the mass moment of inertia J of the rotor in block 16, the motor constant K.sub.e in block 17 and the efficiency ? in block 18 are used to determine the pressure p in block 19.

(14) From the pressure p differentiated in block 20, the pump volume V in block 21 and the compressibility constant ?, the variable V/?*dP/dt is formed in block 23 and fed to block 24. Block 24 is also supplied with the displaced volume V.sub.d from block 26 and the second volumetric flow Q.sub.load, from which the leakage Q.sub.leakage is calculated. In block 25, the leakage Q.sub.leakage is filtered, resulting in the filtered leakage Q.sub.leakage,f.

(15) FIG. 3 shows, with reference to FIG. 1, the diagram 27 formed from the partial diagrams I, II, III over the time t during actuation of the slave cylinder piston 9 of the slave cylinder 8.

(16) Curve 28 shown in partial diagram I shows the displaced volume V.sub.d of the pump 3 over the time t.

(17) The partial diagram II shows the pressure p over the time t. Curve 29 shows a simulated behavior of the hydraulic system 1 according to equation (7). Curve 30 shows the behavior of the pressure of the pump 3.

(18) The partial diagram III shows the leakage Q.sub.leakage over the time t with the leakage simulated based on equation (7) in curve 31, the filtered leakage in curve 32 and the measured leakage of the pump 3 in curve 33.

LIST OF REFERENCE SYMBOLS

(19) 1 Hydraulic system 2 Electric motor 3 Pump 4 Sump 5 Pressure medium 6 Pressure line 7 Switch valve 8 Slave cylinder 9 Slave cylinder piston 10 Arrow 11 Block diagram 12 Block 13 Block 14 Block 15 Block 16 Block 17 Block 18 Block 19 Block 20 Block 21 Block 22 Block 23 Block 24 Block 25 Block 26 Block 27 Diagram 28 Curve 29 Curve 30 Curve 31 Curve 32 Curve 33 Curve A.sub.piston Piston surface area d Damping d/dt Differentiation i Current J Mass moment of inertia K.sub.e Motor constant P Pressure Q.sub.load Second volumetric flow Q.sub.leakage Leakage Q.sub.leakage,f Leakage, filtered Q.sub.pump First volumetric flow t Time V Pump volume V.sub.d Displaced volume x Actuation path {dot over (x)} Actuation speed ? Compressibility constant ? Efficiency {dot over (?)} Angular velocity {umlaut over (?)} Angular acceleration