Abstract:
Within the scope of the method for regulating the rotational speed difference of a switchable frictional engagement control, specially of a clutch or brake, in the driving train of a motor vehicle by means of a control closed loop with the desired rotational speed difference as reference input and the actual rotational speed difference as controlled variable, together with the clutch pressure or brake pressure to be adjusted, at least one other controlled variable is used, wherein the closed loop comprises a linear governor and damping members (TP 1 , TP 2 , TP 3 ) in a manner such that the time shift of the damped variable per reading step does not exceed a predetermined value so that the exciting of the closed loop remains within a stable range for controlling.

Description:
FIELD OF THE INVENTION 
     This invention relates to a method for rotational speed difference regulation of a switchable frictional engagement control. 
     BACKGROUND OF THE INVENTION 
     According to the prior art an automatic transmission contains a hydrodynamic torque converter with converter lock-up clutch, at least one planetary set and two switchable frictional engagement controls in the form of a friction clutch or transmission brake, which serve to transmit torque. 
     Such frictional engagement controls are hydraulically closed. The opening as a rule is assisted by recoil springs. The arrangement of the components described allows a mechanical interruption of the drive train so that the input and output sides are entirely or also partly uncoupled. Said uncoupling divides the rotational speeds on the input from those on the output so that to a certain extent a torsional oscillation uncoupling is also possible. 
     In the present state of the art, frictional engagement controls (clutches, brakes) are used in the automatic transmission for different tasks or functions. One of the most important requirements in all clutch functions is to make possible in all driving modes a comfortable closing. It must here be ensured that the closing be comfortably secured over large rotational speed ranges of engine and output, the same as under different engine torques. 
     Furthermore, there are special operating modes where it is functionally necessary to adjust and maintain on one or more clutches or brakes defined rotational speed differences (slip). The driver must not feel as disturbing the transitions between the separate functions. 
     To satisfy said requirements, conventional solutions distinguish between different load states and depending thereon require changing parameters or even different control structures. 
     The Applicant&#39;s DE 196 06 311 A1 discloses a closed lop control structure which based on a mathematical-physical model of the control system compensates in the form of a front-mounted correction member the essential non-linearities thus arriving in a control technical manner to a linear substitute control systems so that it be possible to use a simple linear governor to guide the controlled variable. Interferences such as outer torques acting upon the clutch are taken into account via a correction member. 
     One disadvantage of this method is the need of knowing a mathematical-physical path model, the quality of which directly influences the control quality attainable. 
     Therefore, this invention is based on the problem of indicating, on the basis of the cited prior art, a method for rotational speed difference regulation of a switchable frictional engagement control in a manner such that without knowing a mathematical-physical model the frictional engagement control so regulated takes over the transition between open and closed state, the same as the adjustment of a defined slip value, wherein the control design for each required utilization of the switchable frictional engagement control is identically constructed and takes care of an increased shifting and, driving comfort. 
     Besides, the inventive method should be utilizable for controlling any torque-transmitting clutches or brakes in the drive train. A linear governor must be used for this. 
     In addition the inventive method must take into consideration a prior existing knowledge of the path model but also in case of incomplete knowledge of the model ensure a sufficient sturdiness and control quality in all operating modes. 
     The method furthermore should allow a defined engine engagement for improving the control quality. 
     SUMMARY OF THE INVENTION 
     It is accordingly proposed, in a closed loop control for regulation of the rotational speed difference of a switchable frictional engagement control and specially of a clutch or of a brake, to provide with the desired rotational speed difference as reference input and the actual rotational speed difference as controlled variable, together with the clutch pressure to be adjusted, at least one other controlled variable and to provide the closed loop control with damping members so that the time shift of the damped variables per reading step does not exceed a predetermined value so that the exciting of the closed loop control remains in the stable range according to control technology. 
     According to the invention the engine torque is preferably used as added controlled variable. 
     It is also possible within the scope of the invention to take into account interferences, specially the actual turbine torque. 
     By using the inventive method the above mentioned disadvantages of the prior art appear no more. Besides, by virtue of he inventive total design switches of the control designs and regulating parameters are no longer needed. 
    
    
     BRIEF DESCRIPTION OF THE DRAWING(S) 
     The invention is described in detail herebelow with reference to the drawing enclosed of a clutch. In the drawing: 
     FIG. 1 is a general closed loop control structure according to this invention; and 
     FIG. 2 is a fundamental representation of the pressure and rotational speed curves when controlling a clutch in the stationary state of the vehicle according to this invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     According to FIG. 1 the desired rotational speed difference Dn_soll is the reference input of the inventive closed loop control. The desired rotational speed difference Δn_soll is here continuously equalized in time by means of a damping member TP 2  or limited to a defined value per reading step so as to prevent unsteadiness in the timed curve of the reference input. TP 2  is preferably designed as low-pass filter. The module ABS services for the absolute value formation prior to calculating the input variable for the governor. 
     The input variable for the governor is the actual control difference. It is formed from the difference between the absolute value of the desired rotational speed difference value and the absolute value of the actual rotational speed difference value of the input and output. From this variable is calculated the pressure value p reg, designated as control portion which acts as direct controlled variable of the linear governor (Governor). 
     To calculate the actual rotational speed difference Δn, the rotational speeds of the clutch input side n_kan and of the clutch output side n_kab are first detected. Before the difference is formed, the variable n_kab is equalized by means of a first damping member and preferably of a low-pass filter TP 1 . A damping of the input rotational speed n_kan can also be optionally provided. The absolute value of the actual rotational speed difference is formed in the module ABS. 
     As already mentioned, thereafter is formed the control difference which corresponds to the sign-provided difference of the absolute values of the actual and desired rotational speed difference. 
     According to the invention, when the difference between the actual rotational speed difference and the dynamic desired value exceeds certain threshold, the engine torque as added controlled variable is reduced via the engine electronics with the aid of the engine engagement according to the control difference. 
     The amount of the reduction is a function of the size of the controlled difference. The engine engagement itself can be implemented by the engine via the standard methods (firing angle engagement, filling change, or others). 
     The necessity of an engine engagement is detected by the module KL_m, the signal for the reduction torque m_red is inputted to module. KL-M, which performs a control difference-reduction torque conversion, and the output of KL-M is passed to the Governor. 
     The manner of the engagement is selected so that the reaction time between the requirement and the actual torque reduction of the input be as short as possible. 
     This engagement reduces the torque to be transmitted to the clutch whereby the adjusting energy to be applied by the governor diminishes. As consequence, the comfort of the closing operation is increased and the clutch linings are less heavily loaded. 
     According to another aspect of this invention, the actual input torque of the clutch is taken into account as interference. This corresponds to the a priori model knowledge and thus describes the states in the actual working point. 
     The interference portion of the clutch pressure p_ST resulting therefrom is converted here from the sign-provided divergence between the actual torque m_an and the working point position m_an_offset, via a calculation block KL_mt, into a corresponding equivalent pressure p st  according to the equation          p   st     =     Δ                 m_an   *     1     μ                     (     Δ                 n     )     ·   r   ·   z   ·     A   K                                    
     with: 
     Δm_an divergence torque at the working point 
     μ(Δn): friction coefficient 
     Δn: rotational speed difference on the clutch 
     r medium frictional radius of the clutch 
     z number of friction linings 
     A K  piston surface 
     p_ST pressure difference calculated on the working point, 
     wherein dynamic pressure portions subject to construction are taken into account by thereafter reducing the variable p_ST by the corresponding dynamic of rotatory pressure portion p_dyn. The rotatory pressure portion p_dyn is calculated from the input rotational speed n_kan in the module KL_pdyn. 
     The time shift of the total adjusting variable clutch pressure which is formed from the control portion p_reg and the interference portion p_ST, is equalized, according to the invention, in the module TP 3  or limited to a defined value per reading step. It is thereby ensured that the exciting of the closed loop remains within the stable range for controlling. 
     As start value for the control phase is used the application or opening pressure of the shifting element p_offset is determined during each shift at the beginning of the control phase. 
     To determine the application or opening pressure of the shifting element p_offset, the procedure is the following: 
     According to FIG. 2 during the clutch control the four phases filling phase, application phase, regulation phase and phase outside the shifting operation are in general differentiated, the rotational speed curves of engine n_mot, primary and secondary pulleys, respectively n_kan, n_kab, and the pressure curve assuming different values in each phase. 
     When the shifting element is pressureless, within the filling phase, before the desired regulation of the rotational speed difference, the clutch/brake must be brought forward to the working point. 
     This is done by the so-called rapid filling with subsequent filling equalizing phase. After the filling phase is terminated, each additional pressure increase leads directly to an increase of the torque transmitted by the clutch. 
     The purpose of the application phase is to find as exactly as possible the working point of the clutch. While in the preceding filling phase the working point can be driven only relatively roughly due to tolerances and time-dependent system parameters, with the application phase a kind of “fine tuning” of the working point takes, place. 
     This occurs by the control carefully touching on the working point, the effect upon the control system being controlled in each step. Consequently, as explained herebelow, the starting values for the control are defined in the control phase by the application phase. 
     During the control phase the clutch is regulated with the object of adjusting a defined rotational speed difference (desired value) or a defined rotational speed difference curve (desired value curve). 
     After termination of the shifting operation, the clutch, in completely closed state, is loaded with a specific pressure according to superposed criteria. The control pressure is here at least strong enough for the clutch to be able to transmit the full input-side torque. 
     The pressure value p_offset is determined according to the operating mode as follows:. 
     a) Change from the state “clutch open: 
     After the already explained filling equalizing phase, the control pressure is gradually increased according to a predetermined gradient within the scope of a control phase until a reaction is to be detected with the aid of the rotational speed difference of input side and output side of the clutch. This reaction consists in that the rotational speed difference diminishes by a defined threshold value. The pressure value predetermined in this state as desired value is used as start value p_offset of the subsequent control phase. 
     b) Change from the state “clutch closed”: 
     The control pressure of the clutch is gradually reduced according to a predetermined gradient until exceeding a threshold value of the rotational speed difference between input and output sides of the clutch whereby an opening of the clutch is indicated. Here is also used as start value p_offset for the subsequent control phase the pressure value predetermined as desired value in this state. 
     Before the total adjusting variable clutch pressure increase by p_offset is superposed on the control system, there results according to the invention as last step in the calculation block KL_reib a correction relative to the rotational speed dependence of the friction coefficient. 
     Within the scope of the inventive method, the clutch in open state is closed for introduction of gear, the filling phase being first carried out in order to bring the clutch in gear. Only after the filling phase is the shifting element led to the desired rotational speed-difference in the control phase. To close the clutch, the desired rotational speed difference is set to zero according to the invention. 
     When within the scope of other functions defined rotational speed differences (slip) are to be adjusted and maintained in the clutch, the work is done with the same control structure. Only the value of the desired rotational speed difference curve (desired value for the control) is modified accordingly. 
     Let it also be mentioned that the inventive method can be used in any torque-transmitting clutch or brake. 
     Within the scope of one variant of the invention, by means of the measured temperature of the transmission oil combined with a mathematical-physical model of the heat input in the slip operation of the clutch, a temperature monitoring of the clutch is effected in order to prevent overheating and thus damage or destruction of the clutch linings. 
     References 
     m anOffset  torque on the frictional engagement control in the working point 
     m an  actual torque on the frictional engagement control 
     n kan  rotational speed primary disc 
     n kab  rotational speed secondary disc 
     Δn soll  desired value of rotational speed difference on the frictional engagement control 
     P Offset  pressure of the frictional engagement control int eh working point 
     P soll  desired pressure on the frictional engagement control 
     m red  reduction torque input 
     TP low-pass filter 
     ABS formation of absolute value 
     governor digital governor 
     Beg step width limitation of the controlled variable 
     K 1   reib  inversely regulated frictional value chracteristic 
     K 1   mt  torque-pressure conversion 
     K 1   m  conversion of control difference-reduction torque 
     nmot engine rotational speed 
     Δm an  divergence torque at working point 
     μ(Δn) frictional value 
     Δn rotational speed difference on the frictional engagement control 
     r central friction radius of the frictional engagement control 
     z number of friction linings 
     A k  piston surface 
     P st  pressure difference calculated on the working point