DE102018211181A1 - Method for determining the control pressure at the point of contact of a regulated starting clutch of an automatic transmission of a motor vehicle - Google Patents

Abstract

A method for determining the control pressure at the point of contact of a regulated starting clutch (2) of an automatic transmission (1) of a motor vehicle is proposed, in which the starting clutch (2) is controlled with an initial pressure that is lower than the control pressure of the starting clutch (2) on Contact point, after which the control pressure is reduced and the starting clutch (2) is actuated with a pressure that is significantly below the control pressure at the contact point, after which cooling of the starting clutch (2) by spraying the starting clutch (2) with gear oil from the Hydraulic circuit of the automatic transmission (1) begins and the actuation pressure of the starting clutch (2) is increased in a ramp-like manner, the actuation pressure being increased until a defined, applicable increase in the cooling oil flow temperature due to the friction in the starting clutch is detected by a temperature sensor (6) being, the difference between the drive pressure at the time of the defined increase in the cooling oil flow temperature and the initial pressure minus an applicable offset corresponds to a learned pressure offset that is valid for the current temperature range of the gear oil.

Description

The present invention relates to a method for determining the control pressure at the point of contact of a regulated starting clutch of an automatic transmission of a motor vehicle according to the preamble of patent claim 1.

It is known from the prior art to detect the contact point of the starting clutch via the engine torque behavior in vehicles comprising an automatic transmission with an integrated regulated starting clutch, while the vehicle is at a standstill in the selector lever position D when braked. First, a reference torque is measured, which indicates how much torque the drive motor, which is designed as an electric motor or internal combustion engine, needs to maintain a predetermined idling speed, while the frictional connection in the transmission is released by the starting clutch. The pressure in the starting clutch is then increased so that the engine has to provide more torque to compensate for the clutch friction. The control pressure at the point of contact is the pressure that is required in the starting clutch in order to load the engine with a predetermined torque, for example approximately 5 Newton meters above the reference torque, while the idling speed remains the same.

To control a starting clutch, a basic pressure characteristic curve is provided over the transmission oil temperature in order to control higher pressures at lower temperatures, so that the changing viscosity of the oil can be compensated. The detected pressure offset from the touch point detection is added to or subtracted from this basic pressure characteristic. The control pressure at the point of contact results from the temperature.

The implementation of the described method can disadvantageously determine the contact points at different transmission oil temperatures, which is caused by a possible temperature drift of the pressure regulator, namely by an unwanted change in the current / pressure position when the ambient temperature changes. Due to a possible temperature drift, identical pressure regulators can set different pressures with the same current control and the same ambient temperature.

Accordingly, it can happen that in a vehicle at lower transmission oil temperatures due to a possible temperature drift of the pressure regulator, a higher clutch pressure is set than required, which means that the engine has to set more torque in order to maintain a predetermined idling speed. In addition, the starting clutch can be heavily loaded due to the increased energy input into the friction elements. Signs of wear of the friction elements caused thereby can lead to increased energy consumption of the drive motor. Furthermore, a possible clutch pressure drift can result in a lower clutch pressure than required, which leads to a delayed creeping of the vehicle due to the underfilled start-up clutch. In such a situation, if the vehicle is on an incline, this can result in an undesired rolling backwards, provided that neither the brake pedal nor the accelerator pedal are actuated in crawl mode.

In order to protect a starting clutch from overtemperature, it is known from the prior art to spray it with transmission oil serving as cooling oil from the hydraulic circuit, as a result of which local heat at the starting clutch, which has arisen, for example, from a differential speed with a lot of torque, is dissipated to the transmission oil becomes.

From the DE 103 16 454 A1 A method for monitoring a clutch of a transmission of a vehicle with an activated crawling function is known, a warning signal being output as a driver warning and / or the clutch transmission properties being adapted when a predetermined limit value of at least one engine and / or transmission size is reached. In the known method, the clutch temperature can be used as the gear unit size, the contact point of the clutch and / or the coefficient of friction being corrected on the basis of the clutch characteristic in order to adapt the clutch transmission properties

From the EP 2 447 561 A2 provides a method for correcting clutch data used to control a friction clutch, the clutch data including the contact point data of the clutch. In the known method, the clutch temperature is detected by means of sensors assigned to the clutch, it being determined whether the clutch temperature takes on values in a predetermined interval and the contact point data of the clutch being updated by a predetermined learning process when the clutch temperature is within the predetermined interval.

From the DE 10 2006 042 958 A1 the applicant knows a device for measuring the oil temperature in a transmission with a temperature sensor, the transmission containing a hydraulic control plate in a transmission housing. It is provided here that the temperature sensor has a heat conductor which is arranged in direct contact with an oil flow and which conducts the oil temperature to the temperature sensor.

The present invention is based on the object of specifying a method for determining the actuation pressure at the contact point of a regulated starting clutch of an automatic transmission of a motor vehicle. The contact point of a starting clutch and thus the required control pressure for different temperature ranges should be determined as precisely as possible.

This object is achieved by the features of patent claim 1. Further embodiments and advantages according to the invention emerge from the subclaims.

• Ansteuern der Anfahrkupplung mit einem Initialdruck, der möglichst in der Nähe des Ansteuerdrucks am Berührpunkt liegt;
• Anfordern einer definierten Getriebeeingangsdrehzahl vom Antrieb;
• Ansteuern der Anfahrkupplung mit reduziertem Druck, der deutlich unter dem Ansteuerdruck am Berührpunkt liegt; der Ansteuerdruck am Berührpunkt ist anhand der Basisdruckkennlinie der Anfahrkupplung mit geringer Genauigkeit bekannt. Die zu diesem Zweck erforderliche Absenkung des Ansteuerdrucks kann beispielsweise rampenförmig erfolgen;
• Nach der Absenkung der Ansteuerdrucks Starten der Kühlung der Anfahrkupplung mittels des Bespritzens der Anfahrkupplung mit Getriebeöl aus dem Hydraulikkreislauf des Getriebes, wobei sich die gemessene Temperatur des Kühlölstroms, nachdem die Anfahrkupplung angespritzt wurde, nicht ändert, da die Anfahrkupplung unter dem Berührpunkt angesteuert ist;
• Rampenförmiges Erhöhen des Ansteuerdrucks der Anfahrkupplung, sodass sich der Ansteuerdruck dem Ansteuerdruck am Berührpunkt nähert und es zu einem Energieeintrag aufgrund der Reibung kommt, wobei die entstehende Wärmeenergie von dem Kühlölstrom aufgenommen und von dem Temperatursensor durch einen Temperaturanstieg des Kühlölstroms erkannt wird;
• Erkennen durch einen definierten, applizierbaren Temperaturanstieg des Kühlölstroms nachdem die Anfahrkupplung angespritzt wurde, welche Kupplungsdruckansteuerung notwendig ist, um die Anfahrkupplung am Berührpunkt zu halten.

Accordingly, a method for determining the control pressure at the point of contact of a regulated starting clutch of an automatic transmission of a motor vehicle is proposed, comprising the following steps:

• Actuation of the starting clutch with an initial pressure that is as close as possible to the actuation pressure at the point of contact;
• Requesting a defined transmission input speed from the drive;
• Actuation of the starting clutch with reduced pressure, which is significantly below the actuation pressure at the contact point; the control pressure at the point of contact is known with little accuracy from the basic pressure characteristic of the starting clutch. The lowering of the control pressure required for this purpose can take place, for example, in the form of a ramp;
• After the control pressure has been reduced, the cooling of the starting clutch is started by spraying the starting clutch with transmission oil from the hydraulic circuit of the transmission, the measured temperature of the cooling oil flow not changing after the starting clutch has been sprayed on, since the starting clutch is activated below the contact point;
• Ramping the activation pressure of the starting clutch so that the activation pressure approaches the activation pressure at the point of contact and there is an energy input due to the friction, the resulting thermal energy being absorbed by the cooling oil flow and detected by the temperature sensor through a temperature rise in the cooling oil flow;
• Recognize through a defined, applicable temperature increase in the cooling oil flow after the starting clutch has been molded on, which clutch pressure control is necessary to keep the starting clutch at the point of contact.

The difference between the actuation pressure of the starting clutch at the time of the defined, applicable increase in the cooling oil flow temperature and the initial pressure minus an applicable offset corresponds to a learned pressure offset that is valid for the current temperature range of the transmission oil, whereby the method is carried out in different temperature ranges of the transmission oil the pressure offset determined in each case, depending on the transmission oil temperature, is added to a basic pressure characteristic curve of the starting clutch via the signed transmission oil temperature.

To carry out the method, the cooling oil flow temperature of the starting clutch, after the cooling oil has been sprayed against the starting clutch, is measured by means of a temperature sensor. The method is carried out when the temperature of the starting clutch corresponds to the cooling oil flow temperature, which is the case when the starting clutch has been closed for a long time, for example when driving in fixed gears for a long time without a slipping starting clutch.

The method according to the invention can be carried out over the entire temperature range of the transmission oil in order to determine separate pressure offsets for defined temperature sections for the starting clutch. In this way, individual pressure regulator deviations of the starting clutches caused by a temperature drift are compensated for across all transmissions.

• 1: Eine schematische Darstellung eines Antriebsstrangs eines Kraftfahrzeugs umfassend ein Automatgetriebe und eine geregelte Anfahrkupplung; und
• 2: Die Verläufe der Temperatur des Kühlölstroms und des Ansteuerdrucks der Anfahrkupplung als Funktion der Zeit zur Veranschaulichung des erfindungsgemäßen Verfahrens.

The invention is explained in more detail below by way of example with reference to the accompanying figures. The same reference numerals designate the same components. Show it:

• 1 : A schematic representation of a drive train of a motor vehicle comprising an automatic transmission and a regulated starting clutch; and
• 2 : The curves of the temperature of the cooling oil flow and the actuation pressure of the starting clutch as a function of time to illustrate the method according to the invention.

In 1 is a drive train of a motor vehicle comprising an automatic transmission 1 and a regulated starting clutch 2 shown. The drive motor 3 is via the regulated starting clutch 2 with the gearbox 1 releasably connectable, whereby for cooling the starting clutch 2 the starting clutch 2 can be sprayed with transmission oil serving as cooling oil from the hydraulic circuit; the resulting cooling oil flow is designated 5. The temperature of the cooling oil flow is used to carry out the method according to the invention 5 after the cooling oil against the starting clutch 2 was injected by means of a control 7 connected and behind the starting clutch 2 arranged temperature sensor 6 measured. In 1 the output of the transmission is designated 4.

In 2 curve A represents the course of the temperature T of the cooling oil flow after the cooling oil against the starting clutch 2 was sprayed as a function of time t, curve B showing the course of the control pressure P the starting clutch 2 represents as a function of time t.

The procedure is carried out when the temperature of the starting clutch 2 the cooling oil flow temperature T corresponds to what is the case when the starting clutch 2 was closed for a long time, for example when driving in fixed aisles without slip.

At the beginning of the implementation of the method according to the invention at time t_0, the starting clutch 2 controlled with initial pressure, which is as close as possible to the control pressure at the point of contact, since no point of contact has yet been detected and learned, whereby a defined gearbox input speed is requested from the drive.

Then the control pressure becomes at time t_1 P lowered and the starting clutch 2 with a print P controlled, which is significantly below the point of contact, the pressure reduction can be ramped. After the control pressure has been reduced, the cooling of the starting clutch begins 2 by spraying the starting clutch 2 with gear oil from the hydraulic circuit of the gear 1 ,

The control pressure then becomes at time t_2 P the starting clutch 2 ramped up to the point of contact of the starting clutch 2 to determine, wherein the control pressure is increased until a defined, applicable increase in the cooling oil flow temperature T due to the friction in the starting clutch is detected, which occurs in the example shown at time t_4. The difference between the control pressure at the time of the defined increase in the cooling oil flow temperature T and the initial pressure minus an applicable offset corresponds to a pressure offset learned according to the invention, which is valid for the current temperature range. The applicable offset is the difference between the actuation pressure at the time of the defined increase in the cooling oil flow temperature T and subtracted the initial pressure to compensate for the effect of overdriving the starting clutch to determine the contact point. In order to compensate for a temperature drift effect of the pressure regulator, the method according to the invention is used in different temperature ranges of the gear oil and the pressure offset determined is stored as a function of the gear oil temperature. The pressure offsets are added to the basic pressure characteristic curve of the starting clutch using the signed transmission oil temperature.

The cooling oil flow temperature T increases from time t_3 due to the increase in the actuation pressure P , In the example shown, at time t_4, namely when the defined, applicable increase in the cooling oil flow temperature is reached T the control pressure P reduced to avoid hysteresis effects during control.

At time t_5, clutch pressure control begins based on the initial pressure plus the pressure offset learned by carrying out the method according to the invention.

Through the design according to the invention, the energy consumption of the engine and the heat input in the starting clutch can be reduced over the service life. In addition, the starting behavior can be improved and an unwanted rolling backwards of the vehicle on an incline when the brake and accelerator pedal is not actuated in creep mode, due to an underfilled starting clutch, can be avoided.

LIST OF REFERENCE NUMBERS

1

automatic transmission

2

clutch

3

drive motor

4

output

5

Cooling oil flow

6

temperature sensor

7

control

P

control pressure

T

Cooling oil flow temperature

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 10316454 A1 [0007]
• EP 2447561 A2 [0008]
• DE 102006042958 A1 [0009]

Claims (2)

Method for determining the activation pressure at the point of contact of a regulated starting clutch (2) of an automatic transmission (1) of a motor vehicle, characterized in that at the beginning of the implementation of the method the starting clutch (2) is activated with an initial pressure which is lower than the activation pressure of the starting clutch (2) at the point of contact, whereby a defined transmission input speed is requested from the drive, the control pressure then being lowered and the starting clutch (2) being controlled with a pressure which is significantly below the control pressure at the point of contact, with cooling after the control pressure has been reduced the starting clutch (2) begins by spraying the starting clutch (2) with gear oil from the hydraulic circuit of the automatic transmission (1) and the control pressure of the starting clutch (2) is increased in a ramp to determine the control pressure at the point of contact of the starting clutch (2), whereby the control pressure increases for so long is until a defined, applicable increase in the cooling oil flow temperature after the cooling oil has been sprayed against the starting clutch (2) due to the friction in the starting clutch (2) is detected by a temperature sensor (6), the difference between the control pressure at the time the defined increase in the cooling oil flow temperature and the initial pressure minus an applicable offset corresponds to a learned pressure offset that is valid for the current temperature range of the transmission oil, the procedure being carried out in different temperature ranges of the transmission oil and the pressure offset determined in each case depending on the transmission oil temperature is added to a base pressure characteristic curve of the starting clutch via the signed transmission oil temperature and the method is carried out if the temperature of the starting clutch (2) corresponds to the cooling oil flow temperature at the beginning of the method. Method for determining the actuation pressure at the point of contact of a regulated starting clutch (2) of an automatic transmission (1) of a motor vehicle Claim 1 , characterized in that when the defined, applicable increase in the cooling oil flow temperature is reached, the control pressure is reduced in order to avoid hysteresis effects when the starting clutch (2) is activated.

Images