DE102006030142A1 - Method for controlling an automated friction clutch - Google Patents

Abstract

The invention relates to a method for controlling an automated friction clutch, which is designed as a dry clutch and arranged in a power train of a motor vehicle in the power flow between a drive motor designed as a combustion engine and a transmission, wherein the friction clutch during a start-up and at the end of a switching operation by means of a clutch actuator is closed from the opened state in the slip mode with decreasing speed difference (Deltan <SUB> K </ SUB>). To achieve a comfortable and low-load closing operation of the friction clutch, it is provided that a friction coefficient (μ <SUB> K </ SUB>) of the friction clutch increasing with decreasing speed difference (Deltan <SUB> K </ SUB>) affects the torque transmission capability of the friction clutch Friction clutch is largely compensated by a corresponding adjustment of the contact force of the friction clutch.

Description

The invention relates to a method for controlling an automated friction clutch, which is designed as a dry clutch and is arranged in a drive train of a motor vehicle in the power flow between a trained as an internal combustion engine drive motor and a transmission, wherein the friction clutch during a start-up and at the end of a switching operation by means of a clutch actuator is closed from the open state in the slip mode with decreasing speed difference Δn _K.

In a drive train of a motor vehicle, the clutch forms a separable connection of the drive motor to the transmission. Since a trained as an internal combustion engine drive can deliver its power only above a minimum speed, the clutch is initially fully opened during a starting and then closed continuously with engaged starting gear, the clutch to compensate for the applied speed difference .DELTA.n _{K is} transitionally in the slip state. The slipping clutch acts at times on the drive motor braking and accelerating to the input shaft of the gearbox and thus to the motor vehicle.

In a switching operation, the clutch is also fully opened to perform the transmission internal circuit of a load gear in a target gear, so the interpretation of the load gear and the synchronization and insertion of the target gear, largely load-free. At the end of the shift, the clutch is closed again, whereby the drive motor is decelerated at an upshift and accelerated at a downshift. By the timing of the closing operation of the clutch, the control is usually carried out as a function of the current torque M _{M of} the drive motor and the momentarily applied to the clutch speed difference .DELTA.n _K , on the one hand, the heating or the thermal load of the clutch by the in the slip phase incurred friction work as well as the mechanical load of the drive train and the perceived by the vehicle occupant comfort when starting and during switching operations determined.

A designed as a dry clutch friction clutch is in the simplest Case as a passively closable one Single-disc dry clutch executed. In this widespread Coupling type, the input-side part of the clutch is partially through a flywheel connected to the crankshaft of the drive motor with a first friction surface and formed by a pressure plate with a second friction surface, the pressure plate rotatably and axially movable in one with the flywheel-connected clutch basket is mounted as well a usually designed as a diaphragm spring pressure spring in the direction the flywheel is loaded. The output side part of the clutch is formed by a drive disc, which is between the flywheel and the pressure plate is arranged, riveted on both sides or glued friction linings is provided, and rotatably and axially displaceable on the input shaft the gearbox is mounted.

In the unactuated idle state, the drive plate is clamped by the action of the pressure spring between the flywheel and the pressure plate with a Überanpressung and thus the clutch completely closed, so that the maximum torque M _{M_max} the drive motor is securely transmitted under all operating conditions (M _{K_max} > M _{M_max} ) , The clutch actuation, so the opening and closing of the friction clutch, via a clutch plate, which may be hydraulically, pneumatically, electromotively or electromagnetically effective. In a training as Zentralausrücker this clutch actuator can also act directly or, in an external arrangement, via a lever mechanism in each case via a release bearing on the pressure spring. In today's conventional design of the pressure spring as a diaphragm spring, the clutch actuator presses on the release bearing in the direction of the drive motor to radially inner spring tongues of the diaphragm spring, whereby the radially outer region of the diaphragm spring is moved in the direction of the gearbox. As a result, the clamping of the drive plate is first reduced, whereby the transmittable torque M _{K of} the clutch is reduced, and finally completely removed, so that the drive plate against the flywheel and the pressure plate freely rotatable and the clutch is thus fully open (M _K = 0 ).

For automated control of a friction clutch, the relationship between the manipulated variable of the clutch actuator and the transmittable torque M _{K of} the clutch is reproduced in the form of at least one characteristic that is stored in a data memory of an associated clutch control unit. In a path-controlled clutch actuator, the manipulated variable is formed by the travel of the clutch actuator or connected to the clutch actuator transmission element, said travel in a passively closable clutch can also be referred to as Ausrückweg. In a pressure-controlled clutch actuator, which is preferably designed as a hydraulic or pneumatic actuator cylinder, however, the manipulated variable is formed by the effective in the clutch actuator control pressure.

Due to the frictional heat occurring in the slip mode of the clutch and because of the heat transfer from other units, in particular from the drive motor, the clutch is exposed to different operating temperatures, which generally lead to changes in the characteristic operating characteristics, such as the gripping point and the friction coefficient μ _K. In order to chen ermögli the most accurate and comfortable for the vehicle occupants control of the respective clutch, some methods for controlling an automated friction clutch have been developed in which determines the operating temperature of the clutch and a temperature-dependent adaptation of the associated control characteristic of the clutch can be performed. For example, in the DE 101 55 459 A1 proposed a method in which the temperature of a friction clutch can be determined without an immediate sensory detection, thereby inter alia to correct the gripping point and the friction coefficient μ _{R of} the friction clutch for automated control. A similar procedure is from the DE 10 2004 029 558 A1 It is known that the gripping point and the friction coefficient μ _{K of} an automated friction clutch are used as so-called adaptation parameters, which are adapted to current values, inter alia, as a function of a temperature increase and a friction power introduced into the clutch. This is intended to achieve an improved accuracy of the control of a friction clutch in conjunction with largely harmonic load changes.

In the known methods the effect known per se, however, is not considered that relatively increases strongly during a closing operation of a clutch designed as a dry friction clutch, the friction coefficient μ _K at the end of the closing operation in a smaller speed difference .DELTA.n _K. This effect can be explained physically by the fact that the microscopic roughnesses of the frictional surfaces which are in frictional engagement engage each other more intensively at low relative speed, that is to say at a small rotational speed difference Δn _K , than at high relative speed. In practice, this results in an asymptotic transition between the lower sliding friction coefficient μ _{K_GR} and the larger static friction coefficient μ _{K_HR of} the friction _clutch .

Therefore, if the friction clutch is closed at a starting or at the end of a switching operation with a constant closing speed, this leads towards the end of the closing process to a progressive increase of the transmittable torque M _{K of} the clutch. As a result, the drive motor is briefly braked for a short time in a startup and an upshift and the input shaft of the gearbox and thus accelerates the vehicle jerky. In a downshift, the drive motor is accelerated for a short time in a corresponding manner and the input shaft of the gearbox and thus the vehicle delayed jerky. This start-up or shift shock represents a high load on the components of the entire drive train and is perceived by the vehicle occupants as unpleasant.

In front In this background, the invention is based on the object Specify a method by which a closing process of an automated Friction clutch of the type mentioned under avoidance or at least weakening a start or shift shock harmonic takes place.

To solve this problem, the invention according to the features of the main claim is based on a method for controlling an automated friction clutch, which is designed as a dry clutch and arranged in a drive train of a motor vehicle in the power flow between a drive motor designed as an internal combustion engine and a transmission, wherein the friction clutch during a starting process and at the end of a switching operation by means of a clutch actuator from the open state in the slip mode with decreasing speed difference .DELTA.n _{K is} closed. In addition, it is provided that the closing operation of the friction clutch is controlled such that a with increasing speed difference Δn _K increasing coefficient of friction μ _{R of} the friction clutch is largely compensated for its effects on the torque transmission capability of the friction clutch by a corresponding adjustment of the contact force of the friction clutch.

By taking into account the friction coefficient μ _R , which greatly increases towards the end of the closing process at a very low rotational speed difference Δn _K in the control of the contact force of the friction clutch, the effect of a starting or shifting shock which otherwise frequently occurs during starting and switching operations is at least largely avoided. As a result, not only the ride comfort is increased, but also the components of the drive train are heavily loaded torque peaks avoided.

Since the coefficient of friction μ _{R of} the friction clutch only noticeably increases towards the end of the closing process, ie at a very small rotational speed difference Δn _K , the adjustment of the contact force advantageously begins with reaching or exceeding a predetermined or determined minimum rotational speed difference _{Δn K_min} at the rotatable coupling _components , and ends with the achievement of Slip limit (Δn _K = 0). Thereafter, the friction clutch is completely closed.

By using a minimum speed difference .DELTA.n _{K_min} as a start signal for adjusting the contact force of the friction _clutch an unnecessary delay of the closing operation and thus a high thermal load of the friction clutch is avoided. The definition or determination of the minimum speed difference Δn _{K_min} can be carried out individually for each clutch closing _operation , for example as a function of relevant operating parameters, such as the current torque M _{M of} the drive motor, the current gear ratio and the throttle position representing the driver's power demand.

The Adjustment of the contact force can be done by the closing speed of the Friction clutch is reduced until the slip limit is reached is. For this purpose, the friction clutch in a path-dependent control with a reduced actuating speed of the clutch actuator and at a pressure dependent Control with a reduced control pressure gradient in the clutch actuator closed.

Is possible but it also means that the adjustment of the contact force takes place, that the friction clutch in the parking position at the beginning of the adjustment phase is held until the slip limit is reached. In this case becomes the clutch plate in a path-dependent control of the friction clutch in the adjustment position at the beginning of the adaptation and in a pressure-dependent control the friction clutch on the signal pressure at the beginning of the adjustment held until the slip limit is reached.

It is particularly advantageous, however, if the friction clutch for adjusting the contact force at the beginning of the adjustment phase initially opened further and held in this position until the slip limit is reached, since this can be done relatively late, ie at very small speed difference Δn _K , and thus the closing operation of the friction clutch is thus only slightly delayed. For this purpose, the clutch actuator is controlled in a path-dependent control of the friction clutch at the beginning of adjustment in a more open position and held in this position, and controlled at a pressure-dependent control of the friction clutch at the beginning of the adaptation to a further open clutch corresponding control pressure and on this control pressure held until the slip limit is reached.

One particularly low-jerk and at the same time faster closing process However, the friction clutch also arises when the adjustment the contact force is effected by the friction clutch in a continuous process first further open and subsequently so far closed, until the slip limit is reached. For this becomes the clutch plate in a path-dependent control of the friction clutch first in a further open Position and then controlled in a more closed parking position, and at a pressure-dependent Control of the friction clutch on one of a further open Clutch corresponding signal pressure and then to one another closed clutch corresponding control pressure controlled.

to Clarification of the invention, the description is a drawing with exemplary embodiments attached.

In this shows

1 an inventively controlled closing operation of a friction clutch in a time chart,

2 a conventionally controlled closing of a friction clutch in a time chart and

3 an alternatively controlled closing operation of a friction clutch in a time chart.

In the 1 to 3 is in each case for a passively closed by means of a contact pressure friction clutch, the timing of the control of the particular closing during an upshift of the associated gearbox shown. For this purpose, the curves of the rotational speed n _{M of} the drive motor and the rotational speed n _{GE of} the input shaft of the gearbox over the time t are shown in the upper part of the figures. In the lower part of the figures, the course of the travel x _K for a path-controlled friction clutch and the control pressure p _K for a pressure-controlled friction clutch of the associated clutch actuator over the time t is shown, where with x _K = 0 and p _K = 0 each of the complete closed state of Rei friction clutch and with x _K > 0 and p _K > 0 respectively a fully open or correspondingly partially open or partially closed state of the friction clutch is called.

In 2 the control of the friction clutch is shown with a conventional course of the closing process. The upshift begins at time t0 with the opening of the friction clutch. Thereafter, the design of the load gear and the synchronization and insertion of the target gear within the gearbox. He too follows from the time t0 a load reduction and an at least partial guidance of the engine speed n _M in the direction of the target speed of the target gear.

At time t1, the friction clutch is fully opened. At time t2, the internal gear shift operation is completed and the friction clutch is closed again with a largely constant closing speed. Towards the end of the closing process, due to the increasing coefficient of friction μ _R, there is a progressive increase in the transmittable torque M _{K of} the friction clutch. As a result, the friction clutch reaches its slip limit prematurely at time t3, which leads to a brief strong deceleration of the drive motor and a corresponding acceleration of the input shaft of the gearbox and thus the entire motor vehicle, which is perceived by the vehicle occupants as unpleasant shift shock SR. At a later time t4, the friction clutch reaches its fully closed state.

To avoid such a shift shock SR, as in 3 is shown, the friction clutch initially remain open beyond time t2 until the speed n _{M of} the drive motor by means of the motor control is sufficiently close to the speed n _{GE of} the input shaft of the gearbox, which in 3 at time t2 'is the case. Only then is the friction clutch closed, reaches the slip limit at time t3, and is completely closed at time t4. Since the reduction of the engine speed n _M but due to the large moment of inertia of the drive motor and the indirect control of the drive motor on the influence of the combustion process takes place relatively slowly, this control process takes comparatively long. As a result, the traction-free phase of the upshift and the slip phase of the friction clutch are also very long, which can lead to a thermal overload of the friction clutch.

In contrast, a shift shock according to the inventive method, as in 1 is shown without a significant extension of the control process avoided. Here, after completion of the internal gear shift at time t2, the friction clutch is initially closed relatively quickly until a predetermined or currently determined minimum rotational speed difference _{Δn K_min} at the friction clutch is _reached at time t2 *. Thereafter, the friction clutch in a continuous process is first opened a bit and then closed further. As a result, the slip limit is reached largely without jerk at time t3, and the friction clutch is then fully closed by time t4.

The duration of the control sequence according to the invention 1 corresponds to reaching the slip limit at time t3 in about the time duration of the conventional control sequence after 2 , However, a comfort-reducing and stress-unfavorable shift shock SR is specifically avoided.

M _K

transferable Torque of the friction clutch

M _{K_max}

Maximum transferable torque

M _M

torque of the drive motor

M _{M_max}

maximum Torque of the drive motor

n

rotation speed

n _GE

rotation speed the input shaft of the gearbox

n _M

rotation speed of the drive motor

p _K

actuating pressure of the clutch actuator

SR

shift shock

t

Time

t0

time

t1

time

t2

time

t2 '

time

t2 *

time

t3

time

t4

time

x _K

Travel Range of the clutch actuator

Δn _K

Speed difference at the friction clutch

Δn _{K_min}

minimal Speed difference

μ _R

friction

μ _GR

sliding friction

μ _HR

friction coefficient

Claims (11)

Method for controlling an automated friction clutch, which is designed as a dry clutch and arranged in a drive train of a motor vehicle in the power flow between a drive motor designed as an internal combustion engine and a transmission, wherein the friction clutch during a starting and at the end of a switching operation by means of a clutch actuator from the open state out in the slip mode with decreasing speed difference (Δn _K ) is closed, characterized in that the closing operation of the friction clutch is controlled such that a decreasing speed difference (Δn _K ) increasing coefficient of friction (μ _R ) of the friction clutch with respect to its effects on the torque transmission capability of the friction clutch by a corresponding adjustment of the contact pressure of Reibungskupp largely compensated. A method according to claim 1, characterized in that the adaptation of the contact pressure with the achievement or exceeding of a predetermined or predetermined minimum speed difference (Δn _{K_min} ) started and with the achievement of the slip limit (Δn _K = 0) is terminated, and that the friction clutch below is completely closed. A method according to claim 2, characterized in that the minimum speed difference (Δn _{K_min} ) depending on relevant operating parameters, such as the current torque (M _M ) of the drive motor, the current ratio of the gearbox and the driver's power demand representative of the accelerator pedal position set for each clutch closing operation is or is determined individually. Method according to at least one of claims 1 to 3, characterized in that the adjustment of the contact force characterized that happens, the closing speed the friction clutch is reduced until the slip limit is reached is. Method according to claim 4, characterized in that that the friction clutch in a path-dependent control with a reduced actuating speed of the clutch actuator and at a pressure-dependent Control with a reduced control pressure gradient in the clutch actuator is closed. Method according to at least one of claims 1 to 3, characterized in that the adjustment of the contact force characterized done that the friction clutch in the parking position at the beginning the adaptation is held until the slip limit is reached. Method according to Claim 6, characterized that the clutch plate in a path-dependent control of the friction clutch in the adjustment position at the beginning of the adaptation and in a pressure-dependent control the friction clutch on the signal pressure at the beginning of the adjustment is held. Method according to at least one of claims 1 to 3, characterized in that the adjustment of the contact force characterized takes place, that the friction clutch initially continues to adapt open is held and in this position, until the slip limit is reached. Method according to claim 8, characterized in that that the clutch plate in a path-dependent control of the friction clutch controlled at the beginning of the adjustment in a further open parking position and is held in this position, or that the clutch plate at a pressure-dependent Control of the friction clutch at the beginning of the adjustment to a a further open clutch corresponding control pressure controlled and maintained at this control pressure becomes. Method according to at least one of claims 1 to 3, characterized in that the adjustment of the contact force characterized done that the friction clutch in a continuous process first further open and subsequently continues to be closed until the slip limit is reached. Method according to claim 8, characterized in that that the clutch plate in a path-dependent control of the friction clutch first in a further open Position and then is controlled in a more closed parking position, or that the clutch actuator in a pressure-dependent control of the friction clutch on one of a further open Clutch corresponding signal pressure and then to one another closed clutch corresponding control pressure is controlled.