DE102018131514A1 - Method for determining a temperature of a hydraulic fluid in a hydraulic system - Google Patents

Abstract

The invention relates to a method for determining a temperature of a hydraulic fluid of a hydraulic system, in which the hydraulic fluid (8) is conveyed by a pump (17) to a consumer (11), preferably a clutch slave cylinder. In a method which allows a precise but inexpensive determination of the temperature of the hydraulic fluid, a period (t1, t2, t3) is determined in which a predetermined volume of the hydraulic fluid (8) flows through a valve (24), depending on this Period (t1, t2, t3) on the temperature of the hydraulic fluid (8) is closed.

Description

The invention relates to a method for determining a temperature of a hydraulic fluid of a hydraulic system, in which the hydraulic fluid is pumped to a consumer, preferably a clutch slave cylinder.

From the DE 10 2016 205 890 A1 A method for determining a system temperature of a hydrostatic section of a hydraulic clutch system is known, in which the temperature of the hydraulic fluid referred to as the system temperature is calculated as a function of at least two temperature signals. A temperature signal is measured with a temperature sensor, while the second temperature signal is calculated.

From the as yet unpublished German patent application of the applicant with the file number 10 2018 114 789.9 A drive unit for a drive train of a hybrid vehicle is known, which comprises a hydraulic system which has a clutch device for transmitting a torque from a connected internal combustion engine and / or at least one electrical machine to an output element, a clutch actuator of the hydraulic system being set up to actuate the clutch device and with this is fluidically connected. In addition to the first electrical machine, there is a second electrical machine and an output shaft, a rotor of the second electrical machine being connected to the output shaft in a rotationally fixed manner and a rotor of the first electrical machine for torque transmission being connectable or connected to the coupling shaft with the clutch device is. The hybrid device has an electrically operated reversing pump which drives a hydraulic medium for actuating the consumers via a switching valve.

The invention has for its object to provide a method for determining a temperature of a hydraulic fluid of a hydraulic system, in which a temperature measurement can be completely dispensed with.

According to the invention, the object is achieved in that a period is determined in which a predetermined volume of the hydraulic fluid flows through a valve, the temperature of the hydraulic fluid being inferred as a function of this period. This configuration takes advantage of the fact that the viscosity of the hydraulic fluid changes as a function of the temperature. Since, given different viscosities, a given volume of hydraulic fluid takes different times to pass through the valve, it is therefore possible to draw reliable conclusions about the temperature of the hydraulic fluid.

A predetermined pressure is advantageously set in the clutch slave cylinder and is released via the valve, a change in pressure being monitored. If a certain pressure change is reached, the time can be stopped. The period of time required to adjust the pressure change is used as a measure of the temperature of the hydraulic fluid.

In one embodiment, a measurement of the time period is started when the pressure has fallen below an upper pressure threshold and the time measurement is ended as soon as the pressure has dropped below a lower pressure threshold. On the basis of these predetermined pressure thresholds, inaccuracies in the edge area are masked out when determining the time and a large variance in the measurement result is excluded, so that the temperature of the hydraulic fluid can be reliably concluded on the basis of the measured period.

In a variant, the measured period of time for determining the temperature of the hydraulic fluid is compared with a time-temperature relationship stored in a controller. This is a very simple but convenient means of quickly concluding the temperature of the hydraulic fluid.

In one embodiment, the time-temperature relationship is stored in tabular form. A lookup table is particularly suitable as a table, in which the measured temperatures are stored at certain time values in order to draw conclusions.

In one embodiment, temperature values not contained in the table are determined by interpolation. Thus, the actual temperature of the hydraulic fluid is always reliably determined.

The time-temperature relationship is advantageously determined in a production end function of the hydraulic system and stored in the hydraulic system. Every hydraulic system is given its specific fluid temperature-dependent times. Depending on the design of the hydraulic system, mineral oil or brake fluid can thus be used as the hydraulic fluid.

In one embodiment, the hydraulic fluid controls at least two consumers via the at least two-way valve. This has the advantage that the control logic of the at least two-way valve can switch depending on the specific temperature of the hydraulic fluid.

In one variant, a cooler or heat exchanger and / or a parking lock actuator are used as consumers.

In one development, the clutch slave cylinder is used to actuate a hybrid disconnect clutch in a hybrid drive train, in which an internal combustion engine, a first electric motor arranged on the internal combustion engine side and a second electric motor arranged on the output side output a torque via the hybrid disconnect clutch to an output of the hybrid drive train by or the torque outputted by the first electric motor and / or the second electric motor are forwarded to drive wheels of the hybrid drive train. By using such a highly complex system, consisting of the hydraulic system and the hybrid drive train, it is of particular importance to dispense with additional parts, such as temperature sensors, which reduces the manufacturing costs.

The invention permits numerous embodiments. One of these will be explained in more detail using the figures shown in the drawing.

• 1 ein Ausführungsbeispiel eines hydrostatischen Kupplungsbetätigungssystems,
• 2 eine Prinzipdarstellung eines Hydrauliksystems zur Ausführung des erfindungsgemäßen Verfahrens,
• 3 eine Prinzipdarstellung eines Hybridantriebsstranges im Zusammenwirken mit des Hydrauliksystems gemäß 2,
• 4 ein Ausführungsbeispiel des erfindungsgemäßen Verfahrens.

Show it:

• 1 an embodiment of a hydrostatic clutch actuation system,
• 2nd 2 shows a schematic diagram of a hydraulic system for carrying out the method according to the invention,
• 3rd a schematic diagram of a hybrid drive train in cooperation with the hydraulic system according to 2nd ,
• 4th an embodiment of the method according to the invention.

1 shows a structure of a hydrostatic clutch actuation system 1 for use in a vehicle. The hydrostatic clutch actuation system 1 includes on the encoder side 2nd an actuator control unit 3rd which has a hydrostatic clutch actuator 4th controls. The clutch actuator 4th is about a gearbox 5 with a piston 6 of a master cylinder 7 kinematically connected. If the position of the clutch actuator changes 4th and the piston 6 in the master cylinder 7 along the actuator path to the right is a volume of the master cylinder 7 changed, creating a pressure p in the master cylinder 7 is built up via a hydraulic fluid 8th via a hydraulic line 9 to the subscriber side 10th of the hydrostatic clutch actuation system 1 is transmitted. On the recipient side 10th causes the pressure p the hydraulic fluid 8th in a clutch slave cylinder 11 a path change on a clutch 12 is transmitted to operate them. With the clutch 12 it is a clutch that is open in the non-actuated state, as used, for example, as a hybrid disconnect clutch in hybrid vehicles. The master cylinder 7 is with an expansion tank 13 connected, a connection opening 14 of the master cylinder 7 through the piston 6 of the master cylinder 7 is released when the piston 6 is in a predetermined position.

In 2nd is a schematic diagram of a hydraulic system 16 shown to carry out the method according to the invention. The hydraulic system 16 includes a pump 17th on one side of a coolant line 18th is connected. The coolant line 18th spends the hydraulic fluid 8th , for example oil or brake fluid. to a first consumer 19th in the form of a heat exchanger. To this first consumer 19th becomes the hydraulic fluid 8th spent for cooling or lubrication.

On the other side is the pump 17th with an actuation line 20th connected. The actuation line 20th is prepared to the hydraulic fluid 8th to spend to the second consumer, which acts as the clutch slave cylinder 11 is formed, which is in operative connection with the hybrid clutch 12 a hybrid powertrain 21st stands. Basically, in both lines, like the coolant line 18th and the actuation line 20th the same hydraulic fluid 8th contain. To the actuation management 20th is a parking lock operator as another consumer 22 connected to a parking lock 23 works. A switchable two-way valve 24th is so in the coolant line 18th and / or the actuation line 20th involved that the hydraulic fluid 8th targeted to the parking lock actuator 22 is feedable.

The pump 17th is designed as an electrically driven reversing pump, which enables a first delivery direction to the hydraulic fluid 8th to supply the cooling / lubrication task as required, with the pump 17th the hydraulic fluid in a second conveying direction 8th supplies one or more actuation functions, which in the present example correspond to the clutch and / or parking lock function. The pump 17th is powered by an electric motor 25th driven by a control unit 26 is controlled. The pump 17th , the electric motor 25th and the control unit 26 form an electrical pump actuator. As a hydraulic fluid source 27th a kind of gear sump is used for all consumers. In the actuation line 20th is a pressure sensor 28 arranged, which with the control unit 26 the pump 17th and with this the entire hydraulic system 16 controlling power electronics 29 connected is.

In 3rd is a schematic diagram of a hybrid powertrain 21st shown which is an internal combustion engine 30th and two electric motors 31 , 32 includes. Here are the two electric motors 31 , 32 via the hybrid disconnect clutch 12 connectable. On the input side of the hybrid disconnect clutch 12 is the internal combustion engine 30th rigid with the second electric motor 31 connected, which works as a generator and, if necessary, energy for the first electric motor during the electric journey 32 which provides a vehicle with the hybrid powertrain 21st drives. The first electric motor 32 is on the output side of the hybrid disconnect clutch 12 positioned and with the output 33 of the hybrid vehicle coupled.

In 4th is an embodiment of the inventive method for determining a temperature of the hydraulic fluid 8th in the hydraulic system described 16 shown. There is pressure p represented over time t. In further considerations, it is assumed that the viscosity of the hydraulic fluid 8th is strongly temperature dependent. At the same time determines the viscosity of the hydraulic fluid 8th also their flow speed with, here assumed, constant pipe diameters in the hydraulic system 16 .

For the determination of the flow rate of the hydraulic fluid 8th becomes the clutch slave cylinder 11 at a given pressure p inflated. After that, this pressure p via the switchable two-way valve 24th released, the pressure being measured continuously, as in 4th is shown. A time measurement starts when an upper pressure threshold S _P0 is undercut. The time measurement stops as soon as the pressure drops below a lower pressure threshold SPU. As from the 4th can be seen, the hydraulic fluid behaves at the different temperatures 8th different, since it takes different times to reach a given volume through the two-way valve 24th to promote. For a hydraulic fluid 8th with a temperature of -10 ° C becomes a time t3 needed to get one through the two pressure thresholds S _P0 and SPU reduce the predetermined pressure difference (curve I. ). Curve II describes the behavior of a hydraulic fluid 8th with a temperature of 25 ° C, which is a period t2 needed to promote the given volume. A hydraulic fluid shown in curve III 8th with a temperature of 75 ° C only needs a period of t1 . The periods t3 , t2 , t1 become shorter and shorter the higher the temperature of the hydraulic fluid 8th is. These periods of time t3 , t2 , t1 are compared with a time-temperature relationship, which is in the form of a lookup table in the control unit 26 the pump 17th is stored where certain time periods are assigned to measured temperatures. If a time period is determined that cannot be clearly assigned, intermediate values of the temperature are interpolated.

The lookup table is recorded at a tape end process in the manufacture of the hydraulic system and stored in the hydraulic system. Each hydraulic system is given a specific time dependent on the fluid temperature.

Reference symbol list

1

Clutch actuation system

2nd

Encoder side

3rd

Actuator control unit

4th

Hydrostatic clutch actuator

5

transmission

6

piston

7

Master cylinder

8th

Hydraulic fluid

9

Hydraulic line

10th

Customer side

11

Clutch slave cylinder

12

clutch

13

surge tank

14

Connection opening

16

Hydraulic system

17th

pump

18th

Coolant line

19th

consumer

20th

Actuation management

21st

Hybrid powertrain

22

Parking lock actuator

23

Parking lock

24th

Two-way valve

25th

Electric motor

26

Control unit

27th

Hydraulic fluid source

28

Pressure sensor

29

Power electronics

30th

Internal combustion engine

31

Electric motor

32

Electric motor

33

Downforce

QUOTES INCLUDE IN THE DESCRIPTION

This list of documents listed by the applicant has been generated automatically and is only included for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Patent literature cited

• DE 102016205890 A1 [0002]
• DE 102018114789 [0003]

Claims (10)

Method for determining a temperature of a hydraulic fluid of a hydraulic system, in which the hydraulic fluid (8) is conveyed by a pump (17) to a consumer (11), preferably a clutch slave cylinder, characterized in that a period (t1, t2, t3) It is determined in which a predetermined volume of the hydraulic fluid (8) flows through a valve (24), the temperature of the hydraulic fluid (8) being deduced as a function of this period (t1, t2, t3). Procedure according to Claim 1 , characterized in that a predetermined pressure is set in the clutch slave cylinder (11) and is released via the valve (24), a change in pressure being monitored. Procedure according to Claim 1 or 2nd , characterized in that a measurement of the period (t1, t2, t3) is started when the pressure has _fallen below an upper pressure threshold (S _P0 ) and the time measurement (t1, t2, t3) is ended as soon as the pressure reaches a lower pressure threshold (S _PU ) has _fallen below. Procedure according to Claim 1 , 2nd or 3rd , characterized in that the measured period (t1, t2, t3) for determining the temperature of the hydraulic fluid (8) is compared with a time-temperature relationship stored in a controller (26). Procedure according to Claim 4 , characterized in that the time-temperature relationship is stored in tabular form. Procedure according to Claim 5 , characterized in that temperature values not contained in the table are determined by interpolation. Method according to at least one of the preceding claims, characterized in that the time-temperature relationship is determined in a production end function of the hydraulic system (16) and is stored in the hydraulic system (16). Method according to at least one of the preceding claims, characterized in that at least two consumers (11, 19, 22) are actuated by the hydraulic fluid (8) via an at least two-way valve (24). Procedure according to Claim 8 , characterized in that a cooler or heat exchanger and / or a parking lock actuator are used as consumers (19, 22). Method according to at least one of the preceding claims, characterized in that the clutch slave cylinder (11) is used to actuate a hybrid separating clutch (12) in a hybrid drive train (21), in which an internal combustion engine (30), a first electric motor (31) arranged on the internal combustion engine side and a second electric motor (32) arranged on the output side outputs a torque via the hybrid disconnect clutch (12) to an output (33) of the hybrid drive train (21) by a through the internal combustion engine (30) and / or the first electric motor (31) and / or the second electric motor (33) output torque to drive wheels of the hybrid drive train (21) are forwarded.

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