DE102012223765A1 - Method for stabilizing a coefficient of friction gradient of a clutch in a motor vehicle - Google Patents

Abstract

The invention relates to a method for stabilizing a coefficient of friction gradient of a clutch in a motor vehicle, in which a drive train can be connected to an internal combustion engine by means of a clutch and a torque is transmitted to an output, the drive train having an engaged gear. In a method in which an almost constant positive coefficient of friction gradient is ensured, the clutch is briefly brought into slip when the motor vehicle is traveling in a low load range.

Description

The invention relates to a method for stabilizing a Reibwertgradienten a clutch in a motor vehicle, in which a drive train by means of a clutch with an internal combustion engine is connectable and a torque is transmitted to an output, wherein the drive train has an engaged gear.

Switching and starting clutches used in motor vehicles may generally have variations in the coefficient of friction across their travel time. It is desirable for the coefficient of friction gradient to remain approximately positive over the service life of the clutch. If negative coefficients of friction gradient are generated above the slip speed, frictional vibrations can occur in the vehicle, which significantly affect the driving comfort. Whether negative coefficients of friction arise depends very much on the driving behavior of the respective driver. On the one hand, negative coefficient of friction gradients occur when the clutches are overloaded, on the other hand, when the clutches are loaded almost exclusively with very low load. Under the load with a low load is to be understood in the following driving with speeds of the internal combustion engine of ≤ 2000 revolutions / minute. While the overload of the clutch can be prevented by a sufficient dimensioning of the clutch, the low-load operation can be counteracted only by a anti-spattering. In such anti-skid control, a pulsating axial force is generated at the clutch, which is to compensate for the vibrations occurring due to a negative Reibwertgradienten. However, there is the risk that the phase is shifted and thus the vibration tendency of the motor vehicle can be further amplified when using such anti-reflection control. Even with a positive effect of anti-reflection control, the friction-induced vibrations can not be completely eliminated, but only reduced.

The invention has for its object to provide a method for stabilizing the Reibwertgradienten over the life of a clutch in a motor vehicle, in which the Reibwertgradient is always in the positive range, whereby the vibration tendency of the motor vehicle is completely prevented.

According to the invention the object is achieved in that when driving the motor vehicle in a low load range, the clutch is briefly brought into a slip. Under a slip should be further understood that the two clutch plates of the clutch have a differential speed to each other, which sets a sliding friction between the two clutch plates. Such slip behavior introduces high energy into the clutch fins, thereby heating the clutch fins and burning contaminants such as oil deposits and debris on the surfaces of the clutch linings, resulting in a new surface finish. The lining quality is simultaneously changed by the thermal and mechanical damage, whereby the surface of the coupling is renewed by such wear. In this way, the frictional properties of the clutch are kept approximately constant and the Reibwertgradient always set positive.

Advantageously, the clutch is brought into the slip independently of a driver's request at predetermined time intervals. This has the advantage that the slip can be triggered by simple software measures and thus no additional attention of the driver is required. Due to this automatic procedure, if necessary, a positive coefficient of friction gradient is realized at the coupling.

In one embodiment, the gear at which the clutch is slipped is greater than the second gear. This approach is recommended because at higher speeds a slower acceleration is realized and therefore a power loss, which is realized by the short-term slip operation of the clutch is not immediately noticed by the driver. Thus, this measure is not perceived by the driver as disturbing.

In one variant, a gear which is lower in relation to the engaged gear is simulated by a precisely defined slip in the transmitting clutch. In such a simulation, although the low gear is not actually engaged, but the speed of the internal combustion engine is increased, so that it gives the impression as if the lower gear is engaged. The driver perceives such a procedure as a downshift and thus not disturbing.

A development of the invention relates to a method for improving the Reibwertgradienten of clutches of a dual-clutch transmission of a motor vehicle, which comprises two sub-drive trains, which are each connected by means of a clutch to an internal combustion engine and transmit a torque to an output, wherein during the driving operation of the motor vehicle, a inlaid gear comprehensive active first part of the drive train is coupled via the closed first clutch to the engine, while the inactive second part of the drive train has an engaged further gear. In a method in which the Reibwertgradient always in can be kept positive range, one of the two clutches is set in a slip when driving the motor vehicle in a low load range. The clutch which is set into slippage is thereby freed from impurities and used friction material, which is the cause of a negative coefficient of friction gradient. Since in this slippage a high energy is transferred to the surfaces of the two clutch linings of the respective clutch, the clutch linings are heated and freed their surface from contamination. This results in a positive coefficient of friction gradient, which is kept approximately stable by the repeated adjustment of the slip condition.

Advantageously, the inactive second clutch, regardless of the driver's request and unnoticed by the driver for a predetermined period repeatedly set in the slip. Upon detection of a low load operation by the software, the clutch is automatically de-contaminated, thus providing the positive coefficient of friction gradient approximately constant for further travel.

In one embodiment, the next-lower gear to the partial drive train comprising the active clutch is engaged on the partial drive train containing the inactive clutch. This insertion takes place before the associated inactive coupling is pressed. The insertion of this next-lower gear allows the setting of the differential speed of the clutch discs to each other by coupling the gears of the transmission. The coupling of these gears leads to the formation of the differential speed and the pressing, i. the application of an axial force results in a force transmission between the clutch plates, whereby the desired energy is formed to burn the contaminants on the clutch linings. This has the advantage that the driver has no time disadvantages in a desire for higher driving dynamics. The desire for higher driving dynamics would even be able to be accelerated in this approach, since the clutch travel is already covered by both the active and the inactive clutch.

In one variant, the gear at which the clutch is slipped is greater than the second gear. Since in the higher gears generally a lower dynamic is present, resulting in a slower acceleration of the motor vehicle, such a power takeoff is subjectively perceived by the driver as uncritical.

In a further embodiment, the inactive coupling is set to slip directly or after an overlapping circuit of the two clutches. The overlap circuit is the period in which the active clutch is opened and the inactive clutch is simultaneously closed. In this case, the time can be shortened at which the open clutch is pressed in gear engaged, since the overlap circuit existing friction energy is provided.

Advantageously, the process for improving the Reibwertgradienten is aborted when a high driving dynamics is requested by the driver. This reliably ensures that an acceleration of the vehicle without restrictions is possible.

In one embodiment, a gear which is lower in relation to the engaged gear is simulated on the active clutch by only a partial transmission of the driving force of the internal combustion engine to the clutch. This has the advantage that a higher rotational speed of the internal combustion engine is realized than it is normally actually guaranteed by the engaged gear. This ensures that no influence is exerted on the driving dynamics, since the internal combustion engine in this phase provides an increased engine torque in order to additionally provide the slip performance of the active clutch. The increase of the engine torque is particularly advantageous because this process has no effect on the actual driving dynamics of the engine and remains unnoticed by the driver.

The invention allows numerous embodiments. One of them will be explained in more detail with reference to the figures shown in the drawing.

It shows:

1 : Schematic representation of a drive train of a motor vehicle with a dual-clutch transmission.

1 shows a schematic diagram of a drive train 1 a motor vehicle with a dual-clutch transmission. Here is a drive unit 2 , For example, an internal combustion engine, via a shaft 3 connected to the dual-clutch transmission, which will be described in more detail below.

The dual-clutch transmission consists of two sub-trains. The first sub-line has a first sub-transmission clutch 4 on which to a first part of the drive train 9 leads. The drive unit 2 in the form of the internal combustion engine is also connected to a second sub-branch, which is a second sub-transmission clutch 5 which is connected to a second partial drive train 8th leads. The two partial drive trains 8th . 9 are about an axle differential 10 to a drive axle 11 of the motor vehicle.

In the partial drive trains 8th . 9 Different courses are stored. This is the first partial drive train 9 the odd gears, like 1 . 3 . 5 , on, while the second sub-powertrain 8th the even gears, like 2 . 4 . 6 , includes. When changing from one gear to another gear both sub-transmission clutches must 4 . 5 be operated simultaneously, as by means of the first partial transmission clutch 4 the one gear from the shaft 3 is decoupled while using the second partial transmission clutch 5 the further course with the wave 3 and thus the internal combustion engine 2 is connected. This procedure is referred to as a discrimination circuit.

Each partial transmission clutch 4 . 5 is powered by a partial transmission clutch actuator 6 . 7 actuated. The required actuation energy can be made available either via an electric motor or a hydraulic pump, possibly in combination with an energy store. The partial transmission clutch actuators 6 . 7 are with a control unit 12 which is the partial transmission clutch actuator 6 respectively. 7 if necessary controls. For actuating the partial transmission clutches 4 . 5 is used as a partial transmission clutch actuator 6 . 7 a hydraulic or hydrostatic clutch actuator (HCA - Hydrostatic Clutch Actuator) used, as for example in the DE 10 2010 047 801 A1 or DE 10 2010 047 800 A1 is disclosed.

In addition, the sub-transmission clutch 4 as active and the partial transmission clutch 5 be considered as an inactive coupling. The active partial transmission clutch 4 stands in the frictional connection with the shaft 3 coming from the drive unit 2 is driven. At certain predetermined time intervals and depending on the given driving situation, the still open partial transmission clutch 5 slipped when in gear for a few seconds, ie pressed. The selection of the time intervals is carried out depending on the mileage of the motor vehicle, the mileage, the number of circuits, the driving collective and the like. In the driving situations, a distinction is made between partial load (ie speed of the internal combustion engine ≦ 2000 revolutions / min) or an almost constant speed. Both the selection of the time interval and the driving situation is carried out regardless of the driver's request by one in the control unit 12 dropped software. The period of time for which the inactive partial transmission clutch 5 slipped in gear engaged, depends on the generated switching power or the switching work. So that the driver does not notice anything of this process or that this process has no influence on the driving dynamics of the motor vehicle, the drive unit increases 2 in this time the engine torque to the clutch torque, which at the inactive second partial transmission clutch 5 necessary is. Should the driver in this phase, in which the two partial transmission clutches 4 . 5 are pressed, require a higher driving dynamics, the process is either aborted (if no downshift is planned) by one of the two partial transmission clutches 4 . 5 is opened and the engine torque is adjusted according to the torque given by the accelerator pedal or the process is even used for faster downshifts, as the Lüftweg the inactive part clutch 5 already laid back. In both cases, the full power of the internal combustion engine is used to propel the motor vehicle.

The explained measure for increasing the coefficient of friction or the setting of a positive coefficient of friction gradient becomes at the inactive partial transmission clutch 5 preferably always set only when higher gears are realized. Among the higher gears, one gear is understood to be greater than the second gear. At the same time, the next-lower gear on the initially inactive sub-transmission clutch 5 inserted before this coupling is pressed.

It is particularly advantageous if, in such a dual-clutch transmission, the proposed measure is carried out directly before or after the overlapping circuit, since the friction circuit already produces friction energy which determines the time with which the inactive partial transmission clutch 5 is pressed in gear, shortened.

Alternatively, during the distinction circuit or already engaged gear through the active sub-transmission clutch 4 the next lower gear can be simulated by only part of the drive energy from the engine 2 over the wave 3 on the active part drive clutch 4 is transmitted, which is also referred to as slippage of the clutch. The driver will feel such slipping of the clutch in an automatic transmission as a downshift.

The explained method is in a software of the control unit 12 stored for driving the dual-clutch transmission and ensures that in low-load operations on additional, not felt by the vehicle occupant circuits with high switching power or switching work, the coefficients of friction in the partial transmission clutches 4 . 5 be stabilized. This creates no time disadvantages for the driver in a desire for higher driving dynamics.

LIST OF REFERENCE NUMBERS

1

 powertrain

2

 drive unit

3

 wave

4

 Part transmission clutch

5

 Part transmission clutch

6

 Teilgetriebekupplungsaktorik

7

 Teilgetriebekupplungsaktorik

8th

 Part powertrain

9

 Part powertrain

10

 axle differential

11

 drive axle

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been 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.

Cited patent literature

• DE 102010047801 A1 [0021]
• DE 102010047800 A1 [0021]

Claims (10)

Method for stabilizing a coefficient of friction gradient of a clutch in a motor vehicle, in which a drive train ( 1 ) by means of the coupling ( 4 . 5 ) with an internal combustion engine ( 2 ) is connectable and a moment is transmitted to an output, wherein the drive train ( 1 ) has an engaged gear, characterized in that when driving the motor vehicle in a low load range, the clutch ( 4 . 5 ) is briefly put in a slip. Method according to claim 1, characterized in that the coupling ( 4 . 5 ) is put into slippage regardless of a driver's request at predetermined time intervals. A method according to claim 1 or 2, characterized in that a relation to the engaged gear lower gear by a well-defined slip in the transmitting clutch ( 4 ) is simulated. Method for improving coefficients of friction of clutches of a dual-clutch transmission of a motor vehicle, comprising two sub-drive trains ( 8th . 9 ), each by means of a coupling ( 4 . 5 ) with an internal combustion engine ( 2 ) are connectable and transmit a torque to an output, wherein during the driving operation of the motor vehicle of the one engaged gear comprehensive active first part of the drive train ( 8th ) via the closed first clutch ( 4 ) to the internal combustion engine ( 2 ) is coupled while the inactive second sub-powertrain ( 9 ) has a further engaged gear, characterized in that when driving the motor vehicle in a low load range one of the two clutches ( 4 . 5 ) is set in a slip. Method according to claim 4, characterized in that the inactive second clutch ( 5 ) is repeatedly set in the slip for a predetermined period regardless of the driver's request. A method according to claim 4 or 5, characterized in that on which, the inactive coupling ( 5 ) partial drive train ( 8th ) the next-lower gear is engaged to the gear, in which, the active clutch ( 4 ) comprising a partial drive train ( 9 ) is inserted. Method according to at least one of the preceding claims 4, 5 or 6, characterized in that the inactive coupling ( 5 ) directly or after an intersection circuit of the two clutches ( 4 . 5 ) is set in the slip. Method according to at least one of the preceding claims 4 to 7, characterized in that the process for improving the Reibwertgradienten is aborted when a high driving dynamics is requested by the driver. Method according to claim 4, characterized in that at the active coupling ( 4 ) a relation to the engaged gear lower gear by a partial transfer of the driving force of the internal combustion engine ( 2 ) on the coupling ( 4 ) is simulated. Method according to one of the preceding claims 4 to 9 characterized in that the internal combustion engine ( 2 ) during slippage of the clutch ( 4 . 5 ) provides a higher moment.

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