DE102005042363A1 - Automatic gearbox switching control method for motor vehicle, involves determining actual temperature of heated friction switching unit before switching process, and disabling heat treatment of unit based on actual temperature - Google Patents

Abstract

The method involves determining the actual temperature of the heated friction switching unit before a switching process, and computing the rise in temperature caused by the switching process. The switching process is executed, when the determined actual temperature does not exceed a maximum temperature. The heat treatment of the friction switching unit is modified or disabled, when the determined actual temperature exceeds the maximum temperature.

Description

The The invention relates to a method for switching control of an automatic Power shift transmission of a motor vehicle, in which a switching operation between a load level to be designed and one to be loaded Target gear stage temporally overlapped by opening at least one of the load gear stage associated Reibschaltelementes and closing at least one of the target gear ratio associated Reibschaltelementes he follows.

at a power shift of the type mentioned above may be a sufficient act known transmission machines, usually in planetary gear design accomplished is in which in each activated gear each have multiple Reibschaltelemente, as clutches and shift brakes, are closed, and at at least one time overlapped when changing the gear stage the load gear assigned frictional shift element open and one of the target gear assigned Friction shift element closed becomes. In such automatic gearboxes are the clutches and shift brakes usually as hydraulically controllable multi-disc clutches or disc brakes executed. For automatic gearboxes of older design can the shift brakes can also be designed as hydraulically actuated band brakes.

Of Further, it may also be in the considered power shift transmission to act a dual-clutch transmission, in which two, each of the Input shaft of one of two partial transmissions associated engine clutches are present, as a hydraulically controllable multi-plate clutches or may be designed as dry clutches. at a dual-clutch transmission is the transition of the power flow from the load gear to the target gear at a normal, i. between two courses different part gear shifting gear change after internal transmission of the target gear and before the internal transmission Designing the load profile by the time-overlapping opening of the the partial transmission of the load gear associated engine clutch and closing the the engine part of the target gear associated engine clutch.

The switching operations Thus, the same take place in both transmission types in the same way, wherein the torque in each case by the time-overlapping and slip-prone opening a first, the load gear stage associated Reibschaltelementes and through the closing a second, the target gear stage associated Reibschaltelementes is redirected. For the standardization of the designations is in In this context, the term of the friction switching element always follows used, which in the case of the dual-clutch transmission in each case the relevant Engine clutch is meant.

During the switching operations in the aforementioned powershift transmissions occurs due to the friction slip to a significant increase in temperature on the friction linings of participating friction shift elements. This is the thermal load with frequent switching operations using the same Reibschaltelemente still increased, as a adequate cooling between shifts often not possible is. This is especially true for the Dual clutch transmission too, as opposed to this type of transmission to the automatic gearbox design always with each switching operation the same Reibschaltelemente be used.

But even with automatic gearboxes can the same Clutches and switching brakes used briefly in a row be, e.g. when activated kickdown function first a or two gear steps down and then under high load the same gears as the is switched up, or when in manual shift mode of one Driver is repeatedly switched back and forth between two gear levels.

The Thermal stress represents the greatest wear and damage influence for the Reibschaltelemente is and should be to avoid malfunction and to achieve an acceptable service life of the respective power shift so low as possible being held.

From the DE 100 43 420 A1 Now, a method for shift control of a power shift transmission is known, according to which the engine torque of the drive motor and the clutch torque of a friction clutch is changed in order to reduce the heating of the friction clutch. Among other things, according to the known method it is provided that the temperature of the friction clutch is monitored, and that measures are taken to reduce the temperature of the friction clutch after a too high temperature has been detected.

This but is associated with the disadvantages that, due to the already achieved high temperature damage the friction clutch can already have occurred, and that the measures envisaged to reduce the temperature can only affect subsequent switching operations.

Moreover, the known method is based on a powershift transmission according to DE 198 59 458 A1 limited, which is designed as a gearbox in countershaft design, and in which acting as a power-shift clutch friction clutch parallel to the clutch of a gear gear, esp special on the idler gear of the highest gear, is arranged. Thus, the known method and parts of the same by design is not readily transferred to powershift transmission of the type considered here with overlapped switching operations at least two Reibschaltelemente.

It is therefore the object of the present invention, a method for shift control of a power shift transmission of the aforementioned Specify type, with the thermal overload of the Reibschaltelemente reliable can be prevented.

The solution of the problem is in conjunction with the features of the preamble of claim 1 is that before each switching determines the current temperature of the friction shift elements involved in the shift and their estimated by the intended switching temperature increase is estimated that is then checked whether at Performing the switching operation in one of the Reibschaltelemente a predetermined maximum temperature T _{max is} exceeded, and that the switching operation in the case of not exceeding the maximum temperature T _max is carried out as intended, and in the case of exceeding the maximum temperature T _max to reduce the heating of the Reibschaltelemente modified or is locked. Instead of the mentioned estimation of the temperature increase, it is also possible to provide a calculation of the energy input made by the switching operation, for example taking into account the rotational speeds, the torque and pressures at the switching element, and taking into account the ambient or oil temperature.

By the determination of the expected by the switching operation heating the Reibschaltelemente before performing the switching operation can an overheating the Reibschaltelemente early be detected and thus a temperature damage of the Reibschaltelemente, in particular the friction linings are reliably prevented.

advantageous Embodiments of the method according to the invention are the subject explained below under claims 2 to 10.

to Determination of the current temperature and the estimation of the Circuit-related increase in temperature of Reibschaltelemente will be useful one software-based Temperature monitoring function used with a mathematical temperature model, in which at least one measured temperature of the power shift transmission, the heating of the Reibschaltelemente in previous switching operations and the cooling of the Friction shift elements after the previous switching operations received.

The Temperature monitoring function, the e.g. implemented in an electronic transmission control unit may be preferred with the commissioning of the motor vehicle started and ended with the parking of the motor vehicle. hereby ensures that the temperature of the Reibschaltelemente monitored seamlessly will and a thermal overload Friction shift elements even under difficult environmental conditions, such as As driving in particularly hot regions, can be avoided.

When Input value of the temperature monitoring function can an operating temperature of a pressure medium of the Reibschaltelemente, like the oil sump temperature the hydraulic pressure medium in hydraulic multi-plate clutches, and / or a housing temperature a close to the Reibschaltelemente housing component be sensory detected. This allows for longer switching pauses, ie outside of circuit-related heating and cooling phases, an approximate Determination of the current operating temperature of the friction switching elements, as a direct measurement, for example, the coating temperatures due the rotating components not possible is.

The Modification of a switching process in case of imminent overheating the Reibschaltelemente is expedient not flat rate and independent of the switching parameters, but as a function of at least the current Temperature of the friction switching elements, the current engine torque, the planned shift speed and the scheduled shift duration.

to Lowering the thermal load of Reibschaltelemente can the engine torque can be reduced, which in the Reibschaltelementen to a lower contact pressure or a lower hydraulic Pressure on the respective friction linings and thus to a lower friction power leads. Likewise, for this purpose, the switching speed can be reduced, thereby the average speed level of the shift reduced and thus also reduced the friction in the Reibschaltelementen becomes.

Furthermore, the shift duration can be reduced, whereby the shifting comfort is worsened, but overheating of the friction shift elements can be prevented by the shorter slip duration. Finally, it is also possible to avoid overheating, instead of a single circuit provided a double circuit, at For example, instead of a single upshift double upshift or perform a double downshift instead of a single downshift. As a result, the speed difference to be bridged on two circuits and the circuit in the case of the automatic transmission is also distributed to a plurality of Reibschaltelemente, so that the thermal load of the friction clutch elements involved is reduced respectively.

in the Case of blocking the intended switching operation should be an optical and / or an audible warning signal is issued to the driver about the to activate activated protection function. The driver can then follow by adapting his driving style, in particular by an appropriate more moderate activity the accelerator pedal in automatic mode and the shift operating elements, like selector lever or paddles in manual mode, impending overheating the Reibschaltelemente and an activation of appropriate protective functions avoid.

to Clarification of the invention, the description is a drawing attached. In this shows

1 several temperature curves in a typical upshift in a time diagram,

2 Gradients of various operating parameters in a typical upshift in a time chart and

3 Gradients of various operating parameters in a typical upshift also in a time chart.

In an upshift in a trained as a gearbox with hydraulic multi-plate clutches and multi-disc brakes and with an upstream hydraulic torque converter power shift occur in a conventional manner in the diagram of 3 shown time profiles of the drive speed n _T and the drive torque M _T to the transmission input shaft and the output speed n _Ab and the output torque M _Ab to the transmission output shaft on. As the output speed n _Ab increases steadily, the input speed n _{T is} lowered to a lower level during the shift operation. Likewise, the output torque M _{Ab is} markedly reduced, whereas the drive torque M _{T is} only slightly reduced.

For this switching operation are the for the on the switching operation 3 involved closing friction switch relevant operating parameters, such as the input speed n _T , the output speed n _Ab and the hydraulic pressure p _H and the relative velocity v _rel in the respective friction switching element in the timing diagram of 2 shown, from which the time courses of the friction power P _R and the temperature T in the Reibschaltelement have been calculated by means of a temperature function.

From the diagram of 1 It is now apparent how, according to the invention, overheating of the friction shifting elements and associated damage, in particular of the friction linings, can be prevented by means of a temperature monitoring function. If an intended switching operation, as represented by the temperature profile of T ₁ , leads to an exceeding of a maximum permissible maximum temperature T _max in one of the involved friction switching elements, this is detected by means of a calculation of the temperature profile before the circuit is carried out and the switching operation for lowering the Temperature modified accordingly.

For example, the engine torque or the drive torque M _T and thus the hydraulic pressure p _H acting on the friction shift element can be lowered so far that the temperature during the shift operation, as in the curve of T ₂ in FIG 1 is shown below the maximum temperature Tmax remains.

It is also possible, as with the curve of T ₃ in 1 is shown to shorten the switching duration, whereby the slip time and thus the friction power P _{R are} reduced, so that the temperature T ₃ during the switching operation remains below the maximum temperature T _max .

By a permanent temperature control all Reibschaltelemente a power shift transmission and derived therefrom activities To avoid heat damage, the life of the Reibschaltelemente and thus the entire power shift essential increase. Furthermore arises, over the lifetime considered, an improvement of shifting comfort due to the now more constant Reibwertverhaltens the switching elements when switching.

M

torque

M _Ab

output torque

M _T

drive torque

n

rotation speed

n _From

Output speed

n _T

Input speed

p

print

p _H

hydraulic pressure

P

power

P _R

friction power

t

Time

T

temperature

T _max

maximum temperature

T ₁

temperature

T ₂

temperature

T ₃

temperature

v

speed

v _rel

relative speed

Claims (10)

A method for switching control of a power shift transmission of a motor vehicle, in which a switching operation between a load gear stage to be engaged and a target gear stage overlapped overlapping by the opening of at least one of the load gear associated Reibschaltelementes and the closing of at least one of the target gear assigned Reibschaltelementes, characterized in that before each switching operation the current temperature of the involved in the switching friction shift elements is determined and estimated by the intended switching operation temperature increase or calculated that is then checked whether a predetermined maximum temperature T _{max is} exceeded when performing the switching operation in one of the Reibschaltelemente, and that the switching operation in the case of not exceeding the maximum temperature T _{max is performed} as intended and in the case of exceeding the maximum temperature T _{max is} modified or disabled to reduce the heating of the friction switch elements. Method according to claim 1, characterized in that that for determining the current temperature and the estimation or Calculation of the circuit-related increase in temperature of the Reibschaltelemente a software-based Temperature monitoring function with a mathematical temperature model is used in the at least one measured temperature of the power shift transmission, the warming the Reibschaltelemente in previous switching operations and the cooling off the Reibschaltelemente go into the previous switching operations. Method according to claim 2, characterized in that that the temperature monitoring function with the commissioning of the motor vehicle started and with the shutdown of the motor vehicle is terminated. Method according to claim 2 or 3, characterized that as an input of the temperature monitoring function at least one operating temperature of a pressure medium of the Reibschaltelemente and / or a housing temperature a close to the Reibschaltelemente housing component sensory is detected. Method according to one of claims 1 to 4, characterized that the modification of the switching process as a function at least the current temperature of the friction shift elements, the current engine torque, the planned shift speed and the scheduled shift duration he follows. Method according to claim 5, characterized in that that the engine torque is reduced. Method according to claim 5 or 6, characterized that the switching speed is reduced. Method according to one of claims 5 to 7, characterized that the switching duration is reduced. Method according to one of claims 5 to 8, characterized that instead of a single circuit, a double circuit, such as double upshift or double reset, carried out becomes. Method according to one of claims 1 to 8, characterized that at a blocking of the intended switching operation, an optical and / or an audible warning is issued.