WO2008000598A1

WO2008000598A1 - Method for controlling an automatic friction clutch

Info

Publication number: WO2008000598A1
Application number: PCT/EP2007/055569
Authority: WO
Inventors: Bernd Döbele; Norbert Wiencek
Original assignee: Zf Friedrichshafen Ag
Priority date: 2006-06-29
Filing date: 2007-06-06
Publication date: 2008-01-03
Also published as: DE102006030142A1

Abstract

The invention relates to a method for controlling an automatic friction clutch which is configured as a dry clutch and is arranged in a drive train of a motor vehicle in the power flux between a drive engine that is configured as an internal combustion engine and a manual transmission, the friction clutch being closed, from the open state, in the slip mode with decreasing rotational speed difference (ΔnK) when the vehicle is started and at the end of a shifting action by means of a clutch actuator. The aim of the invention is to obtain a comfortable closing action of the friction clutch which is free of load impacts. According to the invention, a coefficient of friction (μR) of the friction clutch which increases with decreasing rotational speed difference (ΔnK) is largely compensated for with respect to its effect on the torque transmission of the friction clutch by correspondingly adapting the contact pressure of the friction clutch.

Description

Method for controlling an automated friction clutch

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 designed 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 Kuppiungsstellers from the open state in the slip operation with decreasing speed difference .DELTA.nκ is closed.

In a drive train of a motor vehicle, the clutch forms a separable connection of the drive motor to the transmission. Since a drive motor embodied as an internal combustion engine can deliver its power only above a minimum rotational speed, the clutch is initially fully opened during a drive operation and subsequently continuously closed when the drive gear is engaged, whereby the clutch is temporarily in the skip state to compensate for the applied rotational speed difference .DELTA.k. 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 in an upshift and accelerated at a downshift. Due to the timing of the closing operation of the clutch, the control usually as a function of the current torque M _{M of} the Drive motor and the momentarily applied to UQΓ clutch speed difference An «takes place, on the one hand, the heating or thermal load of the clutch caused by the friction occurring in the slip phase and the mechanical load on the drive train and the perceived by the vehicle occupant comfort when starting and at Switching determined.

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

In unactuated idle state the Mifnehmerscheibe 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 MM max of the Anfriebsmofors under all operating conditions safely transmitted (MK max> MM _. Maχ ) - The Kupplungsbetäfigung, so the opening and closing of the friction clutch, via a clutch plate, which may be hydraulically, pneumatically, electromotively or electromagnetically effective. When trained as Zenfralausrücker this Kuppiungssteller can also directly or, in an external arrangement, via a lifting mechanism respectively act on the pressure spring via a release bearing. In today's usual training of the pressure spring as a diaphragm spring of the coupling divider 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 Mitnehrnerscheibe is first reduced, whereby the transmittable torque MK of the clutch is reduced, and finally completely canceled, so that the drive plate against the flywheel and the pressure plate freely rotatable and the clutch is thus fully open (M _κ = 0) .

For automated control of a friction clutch, the relationship between the manipulated variable of the clutch actuator and the transmittable torque MK of the clutch is reproduced in the form of at least one characteristic, which is stored in a data memory of an associated Kuppiungs- control unit. In a path-controlled Kuppiungssteller the manipulated variable is formed by the travel of the Kuppiungsstellers or connected to the coupling divider transfer element, said travel in a passively closable clutch can also be referred to as Ausrückweg. In a pressure-controlled Kuppluπgsstelier, which is preferably designed as a hydraulic or pneumatic Steilzyiinder, the steep size, however, is formed by the effective in the Kupplungsstelier actuating pressure.

Due to the frictional heat occurring in the coupling operation of the clutch and because of the heat transfer from other units, in particular from the drive motor, the Kuppiung is exposed to different operating temperatures, the Aligemeinen to changes in the characteristic operating characteristics, such as the gripping point and the coefficient of friction μ «, lead , In order to allow as precise as possible and for the vehicle occupants as perceptible comfortable control of the respective clutch Chen, some methods for controlling an automated friction clutch have been developed in which the operating temperature of the clutch determined and a temperature-dependent adaptation of the associated control characteristic of the clutch can be performed. Thus, DE 101 55 459 A1, for example, proposes a method in which the temperature of a friction clutch can be determined without an immediate sensory detection in order to correct inter alia the gripping point and the friction coefficient μ, n of the friction clutch for automated control. A similar method is known from DE 10 2004 029 558 A1, according to which the gripping point and the coefficient of friction μ _{κ of} an automated friction clutch are used as so-called adaptation parameters which, inter alia, depend on a temperature increase and a friction power introduced into the clutch to current values be adapted. 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 method, however, the per se known effect is disregarded that, in a Schiießvorgang designed as a dry clutch friction clutch, the friction coefficient, tiκ towards the end of the closing process at a smaller speed difference ΔΠK relatively strong increases. 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 low rotational speed difference An _K , than at high relative speed. This results in practice in an asymptotic transition between the lower coefficient of friction μκ _.. GR and the larger coefficient of static friction μκ _.. 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 MK 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 torque 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.

Against this background, the object of the present invention is to provide a method with which a closing operation of an automated friction clutch of the type mentioned at the beginning, while avoiding or at least alleviating a starting or shifting shock, takes place more harmoniously.

To achieve this object, the invention proceeds according to the features of the main claim of 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 Krafffluss 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 process mitteis a clutch actuator from the open state in the slip mode with decreasing Drehzahidiffe- is closed Δn _κ . In addition, it is provided that the sliding action of the friction clutch is controlled in such a way that a friction coefficient μπ of the friction clutch increasing with decreasing speed difference Δn _κ with respect to its effects on 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.

By taking into account the end of the Schiießvorgangs at very low speed difference .DELTA.n _κ rapidly increasing friction coefficient μπ in controlling the contact force of the friction clutch of the otherwise frequently occurring with starting and Schaitvorgängen effect of a start-up or scarf Truckes is at least largely avoided. Not only does this increase ride comfort, it also avoids torque peaks that are very damaging to the components of the drive train.

Since the coefficient of friction μ _{R of} the friction clutch only noticeably increases towards the end of the closing operation, ie at a very small rotational speed difference Δn _κ , the adaptation of the contact force advantageously begins with reaching or exceeding a predetermined or determined minimum rotational speed difference ΔΠK _m , _n at the rotatable coupling components , and ends with the reaching of the slip limit (Δn _κ = 0). Thereafter, the friction clutch is fully closed.

By using a minimum speed difference ΔΠK min as a start signal for the adjustment of the contact force of the friction clutch an unnecessary delay of the Schiießvorgangs and thus a high thermal load of the friction clutch is avoided. The determination or determination of the minimum speed difference Δnκ _. mm can be done individually for each clutch closing operation, for example, as a function of relevant operating parameters, such as the current torque MM of the drive motor, the current ratio of the gearbox and the driver's power demand representing Fahrpedalsteliung. The adjustment of the contact pressure can be done by reducing the closing speed of the friction clutch until the slip limit is reached. For this purpose, the friction clutch is closed in a path-dependent control with a reduced Steügeschwindigkeit the clutch actuator and in a pressure-dependent control with a reduced Stelldruckgradienten in the clutch controller.

But it is also possible that the adjustment of the contact force takes place in that the friction clutch is held in the Steliposition at the beginning of the adjustment phase until the slip limit is reached. In this case, the clutch actuator is held at the beginning of the adjustment in a path-dependent control of the friction clutch in the adjustment position at the beginning of the adjustment and a pressure-dependent control of the friction clutch on the Stelidruck until the slip limit is reached.

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

However, a particularly low-jerk and at the same time faster closing operation of the friction clutch also results when the adjustment of the contact pressure occurs in that the friction clutch in a continuous First open the process further and then close it until the slip limit is reached. For this purpose, the Kupplungsstelier is controlled at a path-dependent control of the friction clutch initially in a further open steep position and then in a more closed position, and at a pressure-dependent control of the friction clutch to a further open clutch corresponding control pressure and then to a more closed clutch corresponding control pressure controlled

To illustrate the invention, the description is accompanied by a drawing with exemplary embodiments, In these shows

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

Fig. 2 shows a conventionally controlled closing operation of a friction clutch in a time chart and

Fig. 3 shows an alternatively controlled Schiießvorgang a friction clutch in a time chart.

In FIGS. 1 to 3, the time profile of the control, in particular of the closing operation during an upshift of the associated gearbox, is shown in each case for a friction clutch which is passively closable by means of a pressure spring. For this purpose, in the upper part of the figures in each case the curves of the speed of the drive motor ry and the speed nee the input of the transmission over the time t shown in the lower part of the figures, the course of Steliweges XK for a path-controlled friction clutch and the actuating pressure PK for a pressure-controlled friction clutch of the associated clutch actuator over the time t shown, wherein with XK = 0 and p _κ = 0 respectively the fully closed state of Rei ~ B coupling and with XK> O and PK> O each a fully open or correspondingly partially open or partially closed state of the friction clutch is designated.

In Fig. 2, the control of the friction clutch is shown with a conventional course of the closing operation. The upshift begins at time tθ with the opening of the friction clutch, then takes place within the gearbox laying out the load gear and synchronizing and inserting the target gear. Also takes place from the time tö a load reduction and at least partially guide 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 substantially constant Schiießgeschwindigkeit. 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 Schiupfgrenze 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 shown in Fig. 3, the friction clutch initially remain open beyond time t2 until the speed n ^ of the drive motor by means of the motor control sufficiently close to the speed nβε the input shaft of the gearbox which is the case in Fig. 3 at time t2 '. Only then is the friction clutch closed, reached at time t3 the Closing limit, 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 is avoided by the method according to the invention, as shown in Fig. 1, without a substantial extension of Steuerabiaufs. 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 speed difference Δn _{κ m} in at the friction clutch is reached at time t2 *. Thereafter, the friction clutch is first opened a little bit in a continuous process and then closed more obtuse. 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 time duration of the control sequence according to the invention according to FIG. 1 corresponds to the time duration of the conventional Sfeuerungsabiaufs Fig. 2 until reaching the slip limit at time t3. However, a comfort-reducing and stress-unfavorable shift shock SR is specifically avoided. Bezuαszeichen

M _K Transmittable torque of the friction clutch

Maximum transmittable torque

Torque of the drive motor

Maximum torque of the Aπtriebsmotors n speed ncε speed of Eingangswelie the gearbox

ΠM speed of the drive motor

PK signal pressure of the clutch actuator

SR Switching t Time at time t1 Time t2 Time t2 'Time t2 ^* Time t3 Time

{4 time

XK Steliweg of the coupling operator

Δn _κ speed difference at the friction clutch

^ HK min Minimum speed difference

friction

Sliding friction coefficient μnR static friction coefficient

Claims

claims

1, 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 motor designed as a combustion engine and a transmission, wherein the friction clutch during a starting and at the end of a Schaitvor- gang by means of a Clutch divider from the open state in the eye lupf operation with decreasing speed difference (Δn _κ ) is closed, characterized in that the closing operation of the friction clutch is controlled such that with decreasing Drehzahidiffe- (Διiκ) increasing coefficient of friction (μa) of the friction clutch with respect its effects on the torque transmission capability of the friction clutch is largely compensated by a corresponding adjustment of the contact force of the friction clutch.

2, The method of claim 1, characterized in that the adjustment of Aπpresskraft with the reaching or exceeding a predetermined or certain minimum rotational speed difference _(Δnκ. Min) was begun and to the achievement of the slip limit (An "= 0) is finished, and that the friction clutch is subsequently completely closed.

3, A method according to claim 2, characterized in that the minimum speed difference (Δn « _mιr) ) in dependence on relevant operating parameters, such as the current torque (MM) of the drive motor, the current transmission ratio of the gearbox and representing the power requirement of the driver Fahrpedaistellung each clutch closing operation is specified or determined individually.

4, method according to at least one Ansprücheer claims 1 to 3, characterized in that the adaptation of the contact pressure occurs in that the closing speed of the friction clutch is reduced until the slip limit is reached.

5. The method according to claim 4, characterized in that the friction clutch is closed at a path-dependent Sleueruπg with a reduced actuating speed of the clutch actuator and a pressure-dependent control with a reduced Stelldruckgradienten in the clutch divider.

6, Method according to at least one of claims 1 to 3, characterized in that the adjustment of the contact pressure occurs in that the friction clutch is held in the Steüposition at the beginning of the adjustment until the Schiupfgrenze is reached.

7, A method according to claim 6, characterized in that the clutch plate is held at a path-dependent control of the friction clutch in the Steüposition at the beginning of the adjustment and a pressure-dependent control of the friction clutch on the control pressure at the beginning of the adaptation.

8. The method according to at least one of claims 1 to 3, characterized in that the adaptation of the contact pressure is effected in that the friction clutch is initially opened further at the beginning of the adjustment and is held in this position until the slip limit is reached.

9. The method according to claim 8, characterized in that the clutch actuator is controlled at a path-dependent control of the friction clutch at the beginning of the adaptation in a Weifer open Steueposition and held in this position, or that the clutch plate at a pressure-dependent control of the friction clutch at the beginning άer adjustment is controlled to a further open clutch corresponding control pressure and maintained at this Sfelldruck.

10. The method according to at least one of claims 1 to 3, characterized in that the adjustment of the contact pressure occurs in that the friction clutch in a continuous process initially further opened and then further closed until the slip limit is reached.

11. The method according to claim 8, characterized in that the clutch actuator is controlled in a path-dependent control of the friction clutch first in a further open parking position and then in a more closed parking position, or that the clutch plate at a pressure-dependent control of the friction clutch on one of a further open Clutch corresponding signal pressure and then controlled to a more closed clutch corresponding control pressure.