DE102021207835A1 - Method for diagnosing a starting element of a motor vehicle drive train - Google Patents

Abstract

Method for diagnosing a starting element (B) and for operating a transmission (G) of a motor vehicle drive train, the starting element (B) being replaced by at least one of a plurality of gear-forming shifting elements (A, B, C, D, E) of a transmission (G) is formed, different gear stages (1-8, R) being formed between an input shaft (GW1) and an output shaft (GW2) of the transmission (G) by closing different combinations of the shifting elements (A, B, C, D, E), wherein an incorrectly closed state of the starting element (B) is detected by observing a speed (n_GW) of exactly one transmission shaft (GW), the transmission shaft (GW) being formed neither by the input shaft (GW1) nor by the output shaft (GW2) and with is not directly connected to the starting element (B), as well as electronic control unit (ECU) for carrying out such a method.

Description

The invention relates to a method for diagnosing a starting element of a motor vehicle drive train. The invention also relates to a method for operating a transmission and an electronic control unit for carrying out such methods.

From the U.S. 2008/0017427 A1 a control device for a hybrid vehicle is known. The hybrid vehicle has an internal combustion engine, an electric motor, a first clutch between the internal combustion engine and the electric motor, and a second clutch between the electric motor and the drive wheel. The second clutch is formed by various shifting elements of a multi-stage transmission. The second clutch acts as a starting element during a starting process when the hybrid vehicle is operated with the internal combustion engine. When there is a command to disengage the second clutch or when there is a command to transfer the second clutch to a slip mode, a speed of the electric motor and a speed of the output wheel are used to check whether the second clutch is incorrectly closed. However, with such a procedure, it cannot be clearly identified which of the various switching elements is incorrectly closed. In addition, the ratio between the speed of the electric motor and the speed of the driven wheel changes during the starting process, so that a clear and reliable detection of the incorrectly closed state is subject to errors.

Another way to detect an incorrectly closed starting element is through the DE 10 2009 026 702 A1 described. Therein, an opening error of the starting element is concluded in the event of a sudden torque request from the internal combustion engine or the electric machine, which is not caused by a corresponding actuation of an accelerator pedal and occurs for longer than a specified minimum period of time. However, the erratic torque request can also have other causes, for example an obstacle while driving up an incline, or a hysteresis effect in the clutch control.

There is therefore a need for an improved diagnostic method for detecting an incorrectly closed starting element.

A method according to patent claim 1 and an electronic control unit according to patent claim 10 are proposed for the solution. Advantageous configurations emerge from the dependent patent claims, the description, and from the figures.

A method for diagnosing a starting element of a motor vehicle drive train is specified. The starting element is formed by at least one of several gear-forming shifting elements of a transmission. The transmission is, for example, an automatic transmission based on a planetary gear set, different gear steps being formed between an input shaft and an output shaft of the transmission by closing different combinations of the shifting elements. The switching elements can be formed by clutches and brakes. That or those of the shifting elements, which, or which form the starting element, is designed as a friction clutch or as a friction brake. A rotational speed difference can be compensated for by a slip operation of the starting element with simultaneous torque transmission between a drive source and an output of the motor vehicle drive train.

According to the invention, it is provided that an incorrectly closed state of the starting element is detected by observing a speed of precisely one transmission shaft. The transmission shaft, the speed of which is monitored, is neither the input shaft nor the output shaft of the transmission and is not directly connected to the starting element.

The invention is based on the knowledge that by observing an individual transmission shaft, a reliable conclusion can be drawn about the state of the starting element. Compared to a conclusion based on a control reaction of another system of the drive train, for example the torque control of an internal combustion engine, the observation of the transmission shaft is considerably faster, since there is no dead time before the control reaction has to be taken into account.

Compared to an inference based on the ratio of two different speeds, there is also improved accuracy, since the ratio of the speeds is variable, and due to the different measurement sections, a time delay error between the underlying sensor signals has to be taken into account.

• - die Drehzahl der Getriebewelle nicht innerhalb einer definierten Zeitdauer ab Beginn eines definierten Steuer-Ereignisses größer als ein erster Grenzwert wird, und/oder wenn
• - die Drehzahl der Getriebewelle bei Erkennen eines definierten Ereignisses nicht größer als ein zweiter Grenzwert ist, und/oder wenn
• - die Drehzahl der Getriebewelle nicht größer als ein dritter Grenzwert ist, falls eine Drehzahl eines Verbrennungsmotors des Kraftfahrzeug-Antriebsstrangs kleiner als ein vierter Grenzwert ist.

An incorrectly closed state of the starting element is preferably inferred if:

• - the speed of the transmission shaft does not become greater than a first limit value within a defined period of time from the start of a defined control event, and/or if
• - the speed of the transmission shaft is not greater than a second limit value upon detection of a defined event, and/or if
• - The speed of the transmission shaft is not greater than a third limit value if a speed of an internal combustion engine of the motor vehicle drive train is less than a fourth limit value.

At least one of the first, second and third limit values is preferably characterized by a standstill of the transmission shaft. This is particularly advantageous when the starting element is designed as a brake.

The defined control event can be, for example, a command to engage one of the gears of the transmission. The defined event can be, for example, an actuation to close one of the shifting elements of the transmission, in particular a pressure ramp, which is provided following a pre-filling phase and a pressure equalization phase of the hydraulically actuated shifting element.

The proposed method is preferably carried out when changing from a neutral or parking gear of the transmission to a forward or reverse driving gear of the transmission. In addition or as an alternative to this, the method is preferably carried out during driving operation of the drive train when one of the gears of the transmission is disengaged to avoid internal combustion engine stalling, specifically during the subsequent attempt to reengage one of the gears.

The proposed diagnostic method can be part of an operating method of the transmission. If an incorrectly closed state of the starting element is detected when the method described above is carried out, the transmission is preferably switched to an emergency operating mode and an error message is output.

In order to achieve the object on which the invention is based, an electronic control unit for controlling functions of a transmission of a motor vehicle drive train is also specified. The electronic control unit has a number of signal inputs and is set up to carry out the method based on the received signal inputs. For this purpose, the electronic control unit has a computing unit that is set up to process and evaluate the signal inputs. The electronic control unit also has signal outputs in order to control actuators of the transmission, for example electromagnetic actuators for controlling hydraulic actuating elements of the transmission. The electronic control unit can be in communication with other electronic control units, for example with an electronic control unit of the internal combustion engine and/or with a higher-level powertrain control unit.

• 1 eine schematische Darstellung einen Kraftfahrzeug-Antriebsstrang mit einem mehrstufigen Getriebe;
• 2 eine Schaltmatrix für ein solches Getriebe; und
• 3 einen zeitlichen Ablauf verschiedener Größen des Antriebsstrangs.

An embodiment of the invention is described in detail with reference to the figures. Show it:

• 1 a schematic representation of a motor vehicle drive train with a multi-stage transmission;
• 2 a switching matrix for such a transmission; and
• 3 a chronological progression of different variables of the drive train.

1 shows a schematic representation of a motor vehicle drive train with an exemplary transmission G. The transmission G is set up to provide different gears between an input shaft GW1 and an output shaft GW2 of the transmission G. The output shaft GW2 is connected to at least one drive wheel DW of the motor vehicle. The gears are provided by selectively locking or keeping shifting elements A, B, C, D, E of the transmission G open. This selective closing or holding open of the switching elements A, B, C, D, E different power flows through planetary gear sets P1, P2, P3, P4 of the transmission G are set.

For this purpose, the input shaft GW1 is constantly connected to a planet carrier of the planetary gear set P2. The output shaft GW2 is constantly connected to a planet carrier of the planetary gear set P4. A sun gear of the planetary gear set P1 is constantly connected to a sun gear of the planetary gear set P2. A ring gear of the planetary gear set P2 is constantly connected to a sun gear of the planetary gear set P3. A ring gear of the planetary gear set P3 is constantly connected to a sun gear of the planetary gear set P4. A planetary gear carrier of the planetary gearset P1 is constantly connected to a ring gear of the planetary gearset P4 via a transmission shaft GW. A speed sensor S_GW is provided for detecting a speed of the transmission shaft GW. By closing the switching element A, the sun gear of the planetary gear set P1 is fixed against a housing GG of the transmission G in a rotationally fixed manner. By closing the switching element B, a ring gear of the planetary gear set P1 is fixed in the same way in a rotationally fixed manner. By closing the switching element C, the input shaft GW1 is connected to the sun gear of the planetary gear set P4. By closing the switching element D, a planetary gear carrier of the planetary gear set P3 is connected to the planetary gear carrier of the planetary gear set P4. By closing the switching element E, the sun gear of the planetary gear set P3 is connected to the sun gear of the planetary gear set P4. Of course, this structure of the transmission G is only to be regarded as an example.

The transmission G can optionally have an electric machine EM, the rotor of which acts on the input shaft GW1. An equally optional separating clutch K0 can be provided for the switchable connection between the input shaft GW1 and a connecting shaft AN of the transmission G. The connecting shaft AN can be connected to an internal combustion engine VM of the motor vehicle.

The shifting elements A, B, C, D, E and the separating clutch K0 are hydraulically actuated. For this purpose, the transmission G has a hydraulic control unit HCU. The control unit HCU includes a pump P, which draws in hydraulic fluid from a sump S and makes it available to a pressure line PL. Electromagnetic actuators V1, V2, V3, V4, V5, V6 are connected to the pressure line PL. By activating the actuators V1, V2, V3, V4, V5, V6, hydraulic fluid from the pressure line PL can be selectively supplied to the shifting elements A, B, C, D, E and the separating clutch K0 in order to close them. The corresponding hydraulics are shown only schematically; pressure control valves etc. that are usually provided are not shown. An electronic control unit ECU is provided for controlling the actuators V1, V2, V3, V4, V5, V6. The electronic control unit ECU is supplied with voltage by an on-board network of the motor vehicle. The vehicle electrical system is shown only schematically in the form of a battery BAT and an electrical ground L2.

2 shows a switching matrix for the in 1 shown transmission G. The switching elements A, B, C, D, E are indicated in the columns of the switching matrix. The rows show forward gears 1 to 8 and a reverse gear R. The circles in the individual cells of the switching matrix show which of the switching elements A, B, C, D, E are to be closed to provide the respective gear 1 to 8, R. In gear G according to 1 forms the switching element B a starting element. During a starting process driven by the internal combustion engine VM, the shifting elements A and C are closed in gear 1, while the shifting element B is operated in slip. This enables a speed equalization between the input shaft GW1 and the output shaft GW2 with simultaneous torque transmission.

3 shows the time course of various variables of the drive train, including a speed n_VM of the internal combustion engine VM, a speed n_GW of the transmission shaft GW and a control signal p_C of the actuator V5 for actuating the switching element C. The in 3 The time course shown visualizes a gear engagement process when changing from a neutral or parking gear of the transmission G to the forward gear 1 when the vehicle is stationary. At a point in time t1, the optional separating clutch K0 is closed, and there is a command from the electronic control unit ECU to engage gear 1, while the internal combustion engine VM is being operated at an idling speed. The actuator V5 is then activated at a point in time t2, so that an in 1 not shown piston chamber for actuating the switching element C is filled. The period between time t2 and a period t3 forms the filling phase and the pressure equalization phase. During this period, the shifting element C does not transmit any torque, except for any drag losses. At time t3, the piston chamber is completely filled, so that the switching element C is closed by the ramp following time t3. From time t4, the switching element C is completely closed.

The switching element A is already pressurized at time t1 and is therefore closed. Since the output shaft GW2 is stationary at time t1, the transmission shaft GW also has no speed and is therefore stationary. As soon as both the shifting element A and the shifting element C transmit torque, the speeds of all shafts of the transmission G are defined, so that a fixed speed ratio between the input shaft GW1 and the transmission shaft GW is defined. As a result, the transmission shaft GW is accelerated from time t3. However, torque is only transmitted between input shaft GW1 and output shaft GW2 when one of the other shifting elements B, D or E is engaged.

In a case in which the switching element B would be in an incorrectly closed state, the rotational speed n_GW of the transmission shaft GW would continue to stand still at time t3. If the shifting elements A and B are closed, then the planetary gear set P1 would be blocked and braked, so that the transmission shaft GW would also stand still. If in such a state the closing process of the switching element C as in 3 shown are continued without further measures, the internal combustion engine VM would stall.

In order to detect an incorrectly closed state of the switching element B, the speed n_GW of the transmission shaft GW is observed. It is not necessary to observe another transmission shaft speed. For example, it is monitored whether the rotational speed n_GW of the transmission shaft GW is greater than a first limit value within a defined period of time from the time t1, ie from the command to engage a gear. If the rotational speed n_GW does not exceed the first limit value for the period of time between the times t1 and t3 plus offset, a faulty closed state of the switching element B can be reliably inferred. In response to this, the closing of the switching element C can be canceled or the separating clutch K0 can be opened in order to prevent the internal combustion engine VM from stalling. As a further consequence, the transmission G can be switched to an emergency operating mode in response to the incorrectly closed state of the shifting element B. An error message is also output.

As an alternative or in addition to considering the transmission shaft speed n_GW from the command to engage a gear, the detection of a defined event can be used. For example, it can be checked whether the rotational speed n_GWab of the pressure ramp for closing the switching element C, which is present after the point in time t3, is greater than zero. The pressure ramp can be detected by detecting the control current of the actuator V5.

As an alternative or in addition to considering the transmission shaft speed n_GW from the command to engage a gear, the speed n_VM of the internal combustion engine VM can be used. If the speed of the internal combustion engine VM is below a limit value after the point in time t3, and if the speed n_GW of the transmission shaft GW is not greater than a limit value at this point in time, it can be concluded that the internal combustion engine VM is beginning to stall due to the incorrectly closed switching element B.

The same relationships also exist when one of the gears 1-8, R of the transmission G is disengaged during driving operation of the drive train to prevent the combustion engine from stalling, in that the transmission G is transferred to a neutral stage, and then re-engaging a of the gear steps is carried out.

The procedure described is not limited to the in 1 shown gear scheme limited. The relationships can also be used in transmissions with a different structure. Also, the method described is not limited to an application in a hybrid drive; in the 1 The electric machine EM shown and the separating clutch K0 are only optional components of the drive train.

Reference List

VM

combustion engine

n_VM

speed of the internal combustion engine

G

transmission

ON

connecting shaft

GW1

input shaft

GW2

output shaft

DW

drive wheel

K0

disconnect clutch

P1 - P4

planetary gear set

GW

gear shaft

n_GW

speed of the transmission shaft

S_GW

speed sensor

A

switching element

B

switching element

C

switching element

D

switching element

E

switching element

p_C

control signal

1 - 8

forward gears

R

reverse gear

EM

electrical machine

GG

Housing

HCU

hydraulic control unit

V1 _V6

actuators

P

pump

pl

pressure line

S

swamp

ECU

Electronic control unit

BAT

battery

L2

electrical ground

QUOTES INCLUDED IN DESCRIPTION

This list of the documents cited by the applicant was generated automatically and is included solely 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

• US20080017427A1[0002]
• DE 102009026702 A1 [0003]

Claims (10)

Method for diagnosing a starting element (B) of a motor vehicle drive train, the starting element (B) being formed by at least one of a plurality of gear-forming shifting elements (A, B, C, D, E) of a transmission (G), by closing various combinations of the switching elements (A, B, C, D, E) different gear stages (1-8, R) are formed between an input shaft (GW1) and an output shaft (GW2) of the transmission (G), characterized in that an incorrectly closed state of the starting element (B) is detected by observing a speed (n_GW) of exactly one transmission shaft (GW), the transmission shaft (GW) being formed neither by the input shaft (GW1) nor by the output shaft (GW2) and with the starting element (B) not directly related. procedure after claim 1 , characterized in that it is concluded that the starting element (B) is incorrectly closed if - the speed (n_GW) of the transmission shaft (GW) does not become greater than a first limit value within a defined period of time from the start of a defined control event, and /or if - the speed I (n_GW) of the gear shaft (GW) is not greater than a second limit value when a defined event is detected, and/or if - the speed I (n_GW) of the gear shaft (GW) is not greater than a third limit value is if a speed (n_VM) of an internal combustion engine (VM) of the motor vehicle drive train is less than a fourth limit value. procedure after claim 2 , characterized in that at least one of the first, second and third limit values characterizes a standstill of the transmission shaft (GW). procedure after claim 2 or claim 3 , characterized in that the control event is a command to engage one of the gears (1-8, R) of the transmission (G). Procedure according to one of claims 2 until 4 , characterized in that the defined event is a control for closing one of the switching elements (C) of the transmission (G). procedure after claim 5 , characterized in that the actuation for closing one of the switching elements (C) is a pressure ramp which is provided after a pre-filling phase and a pressure equalization phase of the hydraulically actuated switching element (C). Procedure according to one of Claims 1 until 6 , characterized in that the method is carried out when changing from a neutral or parking position of the transmission (G) to a forward or reverse driving position of the transmission (G). Procedure according to one of Claims 1 until 7 , characterized in that if, during driving operation of the drive train, one of the gears (1-8, R) of the transmission (G) is disengaged to prevent the internal combustion engine from stalling, the subsequent attempt to reengage one of the gears (1-8, R ) the method for diagnosing the starting element (B) is carried out. Method for operating a transmission (G) of a motor vehicle drive train, the transmission (G) having a plurality of shifting elements (A, B, C, D, E), and by engaging different combinations of the shifting elements (A, B, C, D , E) different gears (1-8, R) are formed between an input shaft (GW1) and an output shaft (GW2) of the transmission (G), with at least one of the shifting elements (A, B, C, D, E) being a starting element (B) of the motor vehicle drive train, by means of which a speed compensation between a drive source (VM, EM) and an output (DW) of the motor vehicle drive train is realized with simultaneous torque transmission, characterized in that if when carrying out the method according to one of the Claims 1 until 8th an incorrectly closed state of the starting element (B) is detected, the transmission (G) is switched to an emergency operating mode and an error message is output. Electronic control unit (ECU) for controlling functions of a transmission (G) of a motor vehicle drive train, characterized in that the electronic control unit (ECU) for carrying out the method according to at least one of Claims 1 until 9 is set up.

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