GB2414776A

GB2414776A - Method of actuating an automatic clutch

Info

Publication number: GB2414776A
Application number: GB0511194A
Authority: GB
Inventors: Thorsten Moehring; Guido Wachsmuth
Original assignee: Volkswagen AG
Current assignee: Volkswagen AG
Priority date: 2004-06-05
Filing date: 2005-06-02
Publication date: 2005-12-07
Anticipated expiration: 2025-06-02
Also published as: JP2005344933A; DE102004027575B3; GB0511194D0; GB2414776B

Abstract

The invention relates to a method of actuating an automatic clutch, whereby the input variables, engine rotational speed (n) and slip (S) between engine and transmission, are used to generate a reference variable (Y) for the position of the clutch, wherein from the engine rotational speed (NMotor) a precontrol value (V) for the clutch position is generated and to said value a correction value (K) is then applied, which is dependent at least upon the variables of slip (S) between engine output and transmission and the load request (LW).

Description

241 4776 I Method of actuating an automatic clutch

Description

The invention relates to a method of actuating an automatic clutch according to the preamble of claim 1. The object of the invention is the control of an automated clutch, in particular for control of the starting process, wherein all slip-affected states of travel, such as e.g. crawling and low-speed behaviour, are also included.

Automated clutches are used in particular in automatic transmissions for vehicles. For automatic transmissions, hydrodynamic converters between engine and transmission are prior art. By means of these converters, the torque generated by the engine is transmitted by means of a hydrodynamic connection to the transmission. Hydrodynamic converters are rotational speed- and slip-dependent owing to their being designed with a fluid connection between the input and the output drive. A further clutch option for automatic transmissions are friction clutches, which are actuated by electric or hydraulic actuators. Here, an actuation of the clutch is effected in accordance with a reference variable that describes the state of engagement of the clutch. The clutch is actuated mechanically, wherein the position of the clutch disks relative to one another is set in accordance with requirements. For this purpose, a control unit triggers an electric or hydraulically operated actuator, which converts the reference variable into a mechanical position of the clutch disks relative to one another. The generation of this reference variable in line with requirements and its conversion into a clutch position is therefore the crucial influence factor for the clutch engagement and l disengagement behaviour of the automatic transmission that is experienced by the driver. This substantially determines the acceptance of this type of power transmission. Operations of the clutch are particularly perceptible in the starting and low-speed behaviour of the vehicle.

Methods of controlling friction clutches are already known, wherein the simplest mechanical conversion is effected by means of a centrifugal force governor. Actuation of the clutch is effected in said case in a rotational speed- governed manner based on the operating principle of the centrifugal force governor. A further method is known from DE 36 06 299. The control of an automatic clutch is in said case controlled as a function of the slip and the request of the driver. An engine rotational speed is controlled in accordance with an accelerator pedal position. Depending on the acceleration value of the accelerator pedal, a setpoint slip value is simultaneously defined by means of a characteristic map. The setpoint slip value is a reference variable for the clutch position.

By rotational speed comparison a measurement of the actual slip value is effected, wherein an actuator adjusts the clutch in accordance with the setpoint slip.

The starting process in said case is crucially dependent on the application of the setpoint slip characteristic map.

The clutch engagement operation is effected in accordance with the acceleration of the accelerator pedal, in which case low-speed and crawling behaviour in particular are realizable only with limited comfort. !

The underlying object of the invention is to provide a method of controlling an automated clutch that is suitable in particular for control of the starting process, wherein all slip-affected states of travel, e.g. crawling and low speed behaviour are also included and controlled with high driving comfort.

Low-speed behaviour in this case relates to the low speed range of the vehicle independently of the actual starting operation and hence of the load disconnection preferably from O to cat 30 kph and determines the connection and/or disconnection of the vehicle from the input drive in this range.

In the method of the described type for controlling automated clutches, this object is achieved according to the invention by the characterizing features of claim 1.

Advantageous developments arise from the combination with the sub-claims.

The method according to the invention for controlling an automated clutch uses the input parameters, engine rotational speed and slip between engine and transmission, to generate a reference variable for the position of the clutch. From the engine rotational speed a precontrol value for the clutch position is generated and to this value a correction value is then applied, which is dependent at least upon the variables of slip between engine output and transmission and the load request. The load request in this case may be generated by the evaluation of the load position sensor. The signal of the actual value of the load is further required in order to identify actual and requested load transfers and load changes (traction/thrust) from load actual value and load request respectively. The method is suitable in particular for comfortable control of the clutch during low-speed travel, so-called crawling and/or low-speed behaviour in low gears.

In a further development of the invention, the correction value may be generated by means of a signal, which evaluates the position and/or change of position and/or rate of change of position of the load position sensor.

In the method according to the invention, the slip between engine output and transmission may be both measured and determined computationally, e.g. by means of a model.

In a particularly advantageous development of the invention, the correction value that influences the speed- dependently generated precontrol value is generated in two stages. To generate the correction value, a performance characteristic number that is dependent upon slip and load request as well as load actual value is generated. There is moreover generation of a converter overshoot, which is generated as a function of the slip and the load request.

Converter overshoot and performance characteristic number in this case have different functions. The structure according to the invention allows good tuning of the control method since performance characteristic number and converter overshoot may be adapted separately. In the performance characteristic number the influence of the load change behaviour is preferably mapped, wherein the converter overshoot is utilized to tune the different influences in full- and partial load. I' 5

A further advantageous development is the standardization of the slip value. This value is generated as the difference of engine rotational speed and transmission rotational speed and is subsequently related to the maximum of the respective rotational speed. By dividing the rotational speed difference by the respective maximum value, the slip does not reach any values greater than 1.

The slip processing is therefore substantially simplified in the control method.

Further details of the invention are described in the drawings by way of diagrammatically illustrated embodiments. These embodiments are merely exemplary developments of the invention that do not limit the field of use of the invention.

These drawings show: Figure 1: a system representation of the method according to the invention in the form of a block diagram and Figure 2: a block diagram of the slip calculation.

Figure 1 shows, as input variables of the method according to the invention, the slip S between engine output and transmission input that is formed from the rotational speeds of the engine NMotor and the transmission NGetriebe, as well as the load request LW. In a first branch of the block diagram a precontrol value V for the setpoint value of the clutch position Y is generated from the engine rotational speed NMotor. This setpoint value may be processed as clutch setpoint torque since usually for automatic clutches a torque interface is realized. Any desired other interfaces may however likewise be activated r 6 by adaptation of the setpoint value. The precontrol value V arises as a function of the clutch hardness 3 in dependence upon the engine rotational speed NMotor. The precontrol value V is then corrected with a correction value K, thereby resulting in the reference variable Y for the position of the clutch, usually the clutch setpoint torque. In a second branch of the block diagram the correction value is generated. This correction value is generated on the basis of the slip S. the load request LW and the load actual value Lot. The correction value K is determined from two partial correction values, the performance characteristic number LZ and the converter overshoot WU. In said case, as a function of the slip S. the load request LW and the load actual value Llst the performance characteristic number LZ is generated. This is then corrected with the converter overshoot generated from slip S and load request LW. The converter overshoot WU in this case is read out e.g. from a characteristic map 2 and may in this case also depend additionally upon the load actual value List. The function of the converter overshoot WU and of the performance characteristic number LZ in said case has different dependences upon slip S. load request LW and load actual value List in order to guarantee good applicability of the control function. In addition, the performance characteristic number is generated in such a way that the load change effects in particular are mapped in a slip- dependent manner. Given a full slip instance (slip = 1), according to definition the performance characteristic number 1 is reached.

The converter overshoot is designed in such a way that the influence of the load range (e.g. partial load or full load) is mapped likewise in a slip-dependent manner. The development in this case is such that, in the event of zero r 7 slip, the influence of the converter overshoot diminishes, i.e. becomes 1. The further tuning of the static behaviour change is effected in such a way that full load contributes more towards an opening of the clutch and in the opposite case, a tendency towards zero load, a more direct response is produced. This has direct consequences on the nature of the clutch engagement characteristic, which is therefore firmly controllable.

The correction value KW is multiplied by the precontrol value V and credited to the setpoint value of the clutch position Y. The clutch is actuated in accordance with the reference variable (setpoint value Y) by means of a suitable, preferably electrically or hydraulically actuated actuator. This actuation may occur in a controlled manner or in a set manner by means of a position control loop.

Figure 2 shows in a block diagram the preferred form of implementation of the slip calculation. Here, in a block DIFF the difference of the engine rotational speed NMotor and the transmission rotational speed NGetrlebe is generated.

Furthermore, in the block MAX the maximum value of the rotational speed (either transmission or engine rotational speed) is selected. The rotational speed difference and the maximum value of the rotational speed are applied as an input variable to the next block DIV and a standardization to the rotational speed determined as greater in each case (S = rotational speed difference/(MAX(engine rotational speed, transmission rotational speed)) is effected. The slip value may therefore assume only values lower than 1.

List of reference characters function/characteristic map converter overshoot 2 function/characteristic map performance characteristic number 3 function V = f(NMotor) NMOtOr rotational speed NGetrlebe transmission S slip LW load request Y reference variable (clutch setpoint torque) V precontrol value correction value LZ performance characteristic number WU converter overshoot Llst load actual value DIFF difference generator DIV division block MAX maximum selection

Claims

Job& I -( Claims 1. Method of controlling an automated clutch, whereby the

input variables, engine rotational speed (n) and slip (S) between engine and transmission, are used to generate a reference variable (Y) for the position of the clutch, characterized in that from the engine rotational speed (NMotor) a precontrol value (V) for the clutch position is generated and to said value a correction value (K) is then applied, which is generated on the basis of a slip (S) between engine output and transmission, the load request (LOO) and the load actual value (List)
2. Method of controlling an automated clutch, whereby the input variables, engine rotational speed (n) and slip (S) between engine and transmission, are used to generate a reference variable (Y) for the position of the clutch, characterized in that a precontrol value (V) for the clutch position arises as a function of the clutch hardness (3) in dependence upon the engine rotational speed (NMotor) and to said value a correction value (K) is then applied, which is dependent at least upon the variables of slip (S) between engine output and transmission and the load request (LW).
3. Method according to claim 1 or 2, characterized in that the correction value (K) for the precontrol value (V) generated from engine rotational speed (NMotor) and clutch position is generated in such a way that at least as a function of the slip (S) and of the load request (LOO) a performance characteristic number (LZ) and a converter overshoot is generated, wherein the

JO

mapping of the input variables of slip (S) and load request (LOO) to the performance characteristic number is different from the mapping to the converter overshoot (WU).
4. Method according to one of the preceding claims, characterized in that, for generating the performance characteristic number, in addition to the slip (S) and load request (LOO) the load actual value (List) is evaluated.
5. Method according to one of the preceding claims, characterized in that the load request (LOO) is generated at least from the evaluation of the load position sensor.
6. Method according to one of the preceding claims, characterized in that the evaluation of the load position sensor that represents the load request (LOO) is generated by acquiring the position and/or change of position and/or the rate of change of position of the load position sensor upon actuation thereof.
7. Method according to one of the preceding claims, characterized in that slip (S) between engine output and transmission is calculated on the basis of measured rotational speed values or determined on the basis of a model.
8. Method according to one of the preceding claims, characterized in that the slip (S) is calculated as a standardized slip value by dividing the difference of the rotational speed of transmission and engine by the respective maximum of the rotational speed (either transmission rotational speed or engine rotational speed).
9. Method according to one of the preceding claims, characterized in that the reference variable (Y) for the position of the clutch is the clutch setpoint torque.