DE102018131108A1 - Method for maintaining a hydraulic fluid pressure level in a hydraulic device - Google Patents

Abstract

The invention relates to a method for maintaining a pressure level of a hydraulic fluid in a hydraulic device, in which at least two consumers (4, 6) and a hydraulic actuator (21) of a hybrid disconnect clutch (20) of a hybrid drive are actuated with the same hydraulic medium (7) by the Hydraulic medium (7) is circulated by a pump (2) via a switching valve (10), the hybrid drive being formed by an internal combustion engine (17) and at least one electric motor (18, 19) which are provided with an output by the hybrid disconnect clutch (20) (23) coupled and decoupled. In a method in which an energy balance is improved and CO exhaust gases are reduced, a pressure (p) in the hydraulic device (1) is set as a function of a required torque capacity of the hybrid disconnect clutch (20).

Description

The invention relates to a method for maintaining a pressure level of a hydraulic fluid in a hydraulic device, in which at least two consumers and a hydraulic actuator of a hydraulic disconnect clutch of a hybrid drive are operated with the same hydraulic medium, in that the hydraulic medium is circulated by a pump via a switching valve, the hydraulic drive from an internal combustion engine and at least one electric motor is formed, which are coupled or decoupled to an output by the hybrid disconnect clutch.

From the as yet unpublished German patent application of the applicant with the file number 10 2018 114 789.9 A drive unit for a drive train of a hybrid vehicle is known, which comprises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.

In a parallel hybrid driving mode, the clutch is completely closed in order to be able to transmit the engine torque directly to the wheels that form the drive. The required oil pressure in the slave cylinder of the clutch actuator is held by a switchable shut-off valve. However, this switchable check valve is not 100% leakproof. The pressure of the hydraulic medium slowly decreases over time, so that the pump must interrupt the actuation of another consumer during continuous driving operation in order to increase the pressure in a slave cylinder that actuates the separating clutch. How out 4th emerges, the reversing pump is switched on when a predetermined fixed pressure threshold is reached in order to rebuild the pressure of the hydraulic fluid. This has the disadvantage that electrical energy for the pump is required for a cyclical increase in the pressure in the slave cylinder of the clutch, this energy requirement having a direct negative effect on CO ₂ emissions from the vehicle.

From the DE 10 2016 213 318 A1 A method for maintaining a pressure level of a hydraulic fluid in a hydraulic arrangement is known, wherein in the hydraulic actuator arrangement a volume flow source is connected to a hydraulic cylinder via a pressure line filled with the hydraulic fluid and the operating point corresponds to a position of the actuator arrangement. The method includes a control hysteresis. This reduces the power consumption of the actuator arrangement in higher load ranges, ie in higher pressure ranges.

The invention has for its object to provide a method for maintaining a pressure level in which the energy consumption of the pump is reduced.

According to the invention, the object is achieved in that the pressure in the hydraulic device is set as a function of a required torque capacity of the hybrid separating clutch. This has the advantage that a variable pressure threshold is used as a trigger for pumping in the hydraulic medium. This variable pressure threshold reduces the energy requirement of the pump, since the pump is only switched on when a corresponding pressure drop is actually detected. A post-pumping frequency is significantly reduced by using the variable pressure threshold. A roar of the internal combustion engine in the event of unintentional refilling of the hydraulic medium is prevented because the torque capacity of the hybrid separating clutch is always sufficient due to this variable pressure threshold.

An engine torque of the internal combustion engine is advantageously monitored and compared with a clutch torque of the hybrid disconnect clutch, a difference being formed between the engine torque and the clutch torque and the switching valve being opened for refilling the hydraulic medium when a differential threshold value is exceeded. By monitoring the engine torque of the internal combustion engine and the subsequent pumping of the hydraulic medium triggered as a function of the engine torque, it is reliably realized that the engine torque of the internal combustion engine is reliably transmitted to the output of the hybrid drive.

In one embodiment, the switching valve for refilling the hydraulic medium remains open until a maximum clutch torque of the hybrid separating clutch is reached. The valve can always remain in the initial position to control the clutch. The pump rotates until the target pressure is reached.

In one variant, a pressure / engine torque characteristic curve is determined in an initialization phase of the hydraulic device, which characteristic curve is stored for the operation of the hydraulic device and adapted during operation of the hydraulic device. This has the advantage that the hybrid drive is based on a control characteristic which is adapted to the real conditions of the hybrid drive. The changes in the hybrid disconnect clutch that occur during operation of the hybrid drive due to temperature, wear and the like are compensated for by adapting the pressure / engine torque characteristic.

In one embodiment, the hydraulic medium is removed from a sump. This simplifies the arrangement of the hydraulic device and enables the connection of still further consumers to the same sump for actuation by the hydraulic medium, which is arranged at a certain height under the pump.

A hybrid drive is advantageously used in which the first electric motor is connected to an output, while the internal combustion engine is rigidly coupled to a second electric motor operating as a generator, the first and second electric motors being coupled or uncoupled by the hybrid disconnect clutch. By using the second electric motor working as a generator, electrical energy is provided for the first electric motor, which is used to electrically drive the hybrid drive. This means that smaller high-voltage batteries can be installed in the hybrid drive.

In one embodiment, a cooler or a heat exchanger is used as the first consumer. By means of a hydraulic line, which also controls the slave cylinder of the clutch actuator, the hydraulic medium flows to a coolant line for supplying, for example, a bearing, a cooler or a heat exchanger.

In a further development, a parking lock actuator is used as the second consumer. This means that another consumer is actuated with the same hydraulic medium.

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

• 1 eine Prinzipdarstellung einer Hydraulikeinrichtung zur Ausführung des erfindungsgemäßen Verfahrens,
• 2 eine Prinzipdarstellung eines Hybridantriebes im Zusammenwirken mit der Hydraulikeinrichtung gemäß 1,
• 3 ein Ausführungsbeispiel des erfindungsgemäßen Verfahrens,
• 4 ein Ausführungsbeispiel eines Verfahrens nach dem Stand der Technik.

Show it:

• 1 2 shows a schematic diagram of a hydraulic device for carrying out the method according to the invention,
• 2nd a schematic diagram of a hybrid drive in cooperation with the hydraulic device according to 1 ,
• 3rd an embodiment of the method according to the invention,
• 4th an embodiment of a method according to the prior art.

In 1 a basic illustration of a hydraulic device for carrying out the method according to the invention is shown. The hydraulic device 1 includes a pump 2nd on one side of a coolant line 3rd is connected. The coolant line 3rd spends a hydraulic medium 7 , for example oil, to a first consumer 4th in the form of a heat exchanger. To this first consumer 4th becomes the hydraulic medium 7 spent for cooling or lubrication.

On the other side is the pump 2nd with an actuation line 5 connected. The actuation line 5 is prepared to the hydraulic medium 7 to a second consumer 6 bring, which as a clutch slave cylinder 21st is formed, which is in operative connection with a hybrid disconnect clutch 20th of a hybrid drive system 16 ( 2nd ) stands. Basically, in both lines, like the coolant line 3rd and the actuation line 5 the same hydraulic medium 7 contain. To the actuation management 5 is still a parking lock operator as another consumer 8th connected to a parking lock 9 works. On-off valve 10th is so in the coolant line 3rd and / or the actuation line 5 involved that the hydraulic medium 7 targeted the parking lock actuator 8th is feedable.

The pump 2nd is designed as an electrically driven reversing pump, which enables a first delivery direction to the hydraulic medium 7 to perform the cooling / lubrication task as required, taking the pump 2nd In a second conveying direction, the hydraulic medium supplies one or more actuation functions, which in the present example correspond to the clutch and / or parking lock function. The pump 2nd is powered by an electric motor 11 driven by a control unit 12 is controlled. The pump 2nd , the electric motor 11 and the control unit 12 form an electrical pump actuator. As a source of hydraulic fluid 13 will be for all consumers 4th , 6 , 8th , used a kind of gear sump. In the actuation line 5 is a pressure sensor 14 arranged, which with the control unit 12 the pump 2nd and via this with power electronics that control the entire drive unit 15 connected.

In 2nd is a schematic diagram of a hybrid drive system 16 shown which is an internal combustion engine 17th and two electric motors 18th , 19th includes. Here are the two electric motors 18th , 19th via the hybrid disconnect clutch 20th connectable. On the input side of the hybrid disconnect clutch 20th is the internal combustion engine 17th rigid with the second electric motor 19th connected, which works as a generator and, if necessary, energy for the first electric motor during the electric journey 18th which provides a vehicle with the hybrid drive system 16 drives. The first electric motor 18th is on the output side of the hybrid disconnect clutch 20th positioned and with the output 22 of the hybrid vehicle coupled.

In 3rd is an embodiment of the method according to the invention for maintaining a pressure level of the hydraulic medium 7 in the hydraulic system 1 shown. A diagram is shown which shows an engine torque Mv the internal combustion engine ( 17th ) and a clutch torque M _K the hybrid disconnect clutch 20th over time t. As a result of a leak in the switching valve 10th the clutch torque is reduced M _K the hybrid disconnect clutch 20th depending on the pressure p of the hydraulic medium 7 . During operation, the engine torque Mv of the internal combustion engine 17th with the clutch torque M _K the hybrid disconnect clutch 20th is monitored and there is a difference between the respective engine torque Mv of the internal combustion engine 17th and the current clutch torque M _K the hybrid disconnect clutch 20th detected.

If it is detected that this difference is a predetermined threshold S1 , S2 falls below, a signal is sent to the pump 2nd and the switching valve 10th issued to refill the hydraulic medium 7 from the gearbox sump 13 into the actuation line 5 to enable. By refilling the hydraulic medium 7 the clutch torque increases M _K the hybrid disconnect clutch 20th at. The pump 2nd and the switching valve 10th are operated until a maximum clutch torque M _Kmax on the hybrid disconnect clutch 20th is present. Then both are switched off.

In the period between t1 and t2 the torque gradient of the hybrid disconnect clutch is reduced 20th due to the leakage of the switching valve 10th . Because the internal combustion engine 17th Uneven torque delivery only occurs at the time t2 when the difference between the clutch torque M _K the hybrid disconnect clutch 20th and the engine torque Mv of the internal combustion engine 17th the threshold S1 falls below, a refill of the hydraulic medium 7 into the actuation line 5 enables.

How out 3rd can be seen, the pressure thresholds vary S1 , S2 that trigger the replenishment of the hydraulic medium 7 be determined at the time t1 and at the time t2 , because at the respective time the internal combustion engine 17th different engine torques Mv applies. This reduces the post-pumping frequency, since the post-pumping is only carried out when it is really necessary.

Because of this solution there is an interruption in the coolant circuit of the first consumer 4th prevented because of the hybrid disconnect clutch 20th actuating slave cylinder 21st only then hydraulic medium 7 is supplied when it is necessary. The number of switching operations between the first consumer 4th and pressure build-up for the slave cylinder 21st is thus reduced, which leads to a reduction in the energy expenditure on the pump 2nd leads.

Reference symbol list

1

Hydraulic device

2nd

pump

3rd

Coolant line

4th

First consumer

5

Actuation management

6

Second consumer

7

Hydraulic medium

8th

Parking lock actuator

9

Parking lock

10th

Switching valve

11

Electric motor

12

Control unit

13

Hydraulic fluid source

14

Pressure sensor

15

Power electronics

16

Hybrid drive system

17th

Internal combustion engine

18th

Electric motor

19th

Electric motor

20th

Hybrid disconnect clutch

21st

Slave cylinder

22

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 102018114789 [0002]
• DE 102016213318 A1 [0004]

Claims (8)

Method for maintaining a pressure level of a hydraulic fluid in a hydraulic device, in which at least two consumers (4, 6) and a hydraulic actuator (21) of a hybrid disconnect clutch (20) of a hybrid drive are actuated with the same hydraulic medium (7) by the hydraulic medium (7) is circulated by a pump (2) via a switching valve (10), the hybrid drive being formed by an internal combustion engine (17) and at least one electric motor (18, 19) which are coupled to an output (22) by the hybrid separating clutch (20) or decoupled, characterized in that a pressure (p) in the hydraulic device (1) is set as a function of a required torque capacity of the hybrid disconnect clutch (20). Procedure according to Claim 1 , characterized in that an engine torque (Mv) of the internal combustion engine (17) is monitored and compared with a clutch torque (M _K ) of the hybrid disconnect clutch (20), a difference between the engine torque (Mv) and clutch torque (M _K ) being formed and the switching valve (10) for refilling the hydraulic medium (7) is opened when a differential threshold value is exceeded. Procedure according to Claim 1 or 2nd , characterized in that the switching valve for refilling the hydraulic _medium (7) remains open until a maximum clutch _torque (M _Kmax ) of the hybrid _separating clutch (20) is reached. Procedure according to Claim 1 , 2nd or 3rd , characterized in that in an initialization phase of the hydraulic device (1) a pressure / engine torque characteristic curve is determined, which is stored for the operation of the hydraulic device (1) and adapted during the operation of the hydraulic device (1). Method according to at least one of the preceding claims, characterized in that the hydraulic medium (7) is removed from a reservoir (14). Method according to at least one of the preceding claims, characterized in that a hybrid drive is used in which the first electric motor (18) is connected to the output (22), while the internal combustion engine (17) is rigid with a second electric motor (19 ) is coupled, the first and the second electric motor (18, 19) being coupled or uncoupled by the hybrid disconnect clutch (20). Method according to at least one of the preceding claims, characterized in that a cooler or a heat exchanger is used as the first consumer (4). Method according to at least one of the preceding claims, characterized in that a parking lock actuator (8) is used as the second consumer (6).

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