Abstract:
Within the scope of the method to improve the automotive stability control in connection with an automotive stability computer and with electronic CVT transmission, the change of the rotatory inertia appearing during control engagement as consequence of a change of ratio of the transmission is eliminated.

Description:
The invention relates to a method improving the automotive stability control relates to electronic continuously variable automatic transmissions (CVT). 
     BACKGROUND OF THE INVENTION 
     The purpose of automotive stability control for the vehicle is to dynamically obtain stable operating states in the physical limiting range. To that end, an automotive stability computer usually engages in the braking system by purposefully braking individual gears and/or in engine management by reduction or removal of engine torque independent of the accelerator pedal value. In the control engagement, each change of the rotary inertia of the power train connected with the gears is an undesired interference level. 
     This invention, therefore, is based on the problem of outlining, on the basis of the cited prior art, a method for improving automotive stability control in connection with electronic CVT transmissions. 
     Accordingly, it is proposed to eliminate the rotary inertia change consequently appearing from a transmission ratio change, to effectively remove a relevant interference level of the automotive stability control. 
     SUMMARY OF THE INVENTION 
     Within the scope of an advantageous embodiment, to implement the inventive method, the automotive stability computer and the electronic transmission control are coupled with each other via the CAN (controller area network) data line or a direct signal line so that a signal indicative of the active engagement of the automotive stability computer is passed on to the electronic transmission control. 
     Based on the principle of continuous variability, every current operation of ratio adjustment in the transmission can be event-controlled, directly changed or discontinued. It is unimportant here in what manner the variator ratio assumes the driving strategy of the vehicle/transmission (usually by means of ratio, rotational speed or output torque controls or by the CVT tip strategy to reproduce discrete ratio steps). 
     With detection of the active automotive stability control, according to the invention use, is made of the above cited principle and the actually existing variator ratio is “frozen” by the electronic transmission control independently of an eventually direct current adjustment so as to eliminate a change of the rotatory inertia due to a change of ratio of the transmission. 
     When the engagement of the electronic transmission control is terminated, a transition function ensures the comfortable transfer to the “normal ratio”. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be described, by way of example, with reference to the accompanying drawings in which: 
     FIG. 1 is a block diagram of a CVT automotive stability system incorporating the present invention; and, 
     FIG. 2 is a flow chart of the method to improve the automotive stability control in connection with electronic controlled CVTs. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, therein is shown a block diagram of an illustrative CVT Automotive Stability System  10  incorporating the present invention. As shown therein, and as described herein above, a CVT Automotive Stability System  10  includes an Automotive Stability Computer  12  and an Electronic Transmission Control  14  that are coupled with each other via a Link  16 , such as the CAN (controller area network) data line or a direct signal line, so that an Engagement Signal  18  indicative of the active engagement or disengagement of the Automotive Stability Computer  12  is passed from the Automotive Stability Computer  12  to the Electronic Transmission Control  14 . Electronic Transmission Control  14  also receives a Ratio Input  20  indicating a desired transmission ratio or change in transmission ratio, and in turn provides a Ratio Control Signal  22  to the Continuously Variable Transmission (CVT)  24  to control the transmission ratio of the CVT  24  according to the method described below with reference to FIG.  2 . 
     Referring to FIG. 2, the method of the present invention is invoked upon the occurrence of a transmission ratio change, which occurs at the start of an initial Step  26 . In Step  26 , the CVT Automotive Stability System  10  initially operates in a Normal Driving Strategy State  28  wherein, as represented in FIG.  2  and for the sake of simplicity, the ratio of the normal driving strategy (i_V_strategy) is designated as ratio standard (i_V_soll). 
     In a next step, indicated as Step  30 , the Electronic Transmission Control  14  detects whether the Automotive Stability Computer  12  is in active engagement or is disengaged. Upon detection of the active automotive stability control (Automotive Stability Computer  12  active), when a Engagement Signal  18  indicating the active engagement has been passed on to the Electronic Transmission Control  14 , the CVT Automotive Stability System  10  enters a Step  32  (yes) wherein the CVT Automotive Stability System  10  is in a Frozen State  34  wherein the actual variator ratio (iV_ist) of the electronic transmission control is “frozen”. At this stage i_V_soll=i_V_ist=constant applies. 
     Termination of the Frozen State  34  of the variator ratio, that is, termination of Step  32 , is indicated by the Engagement Signal  18  of the Automotive Stability Computer  12  that shows the end of activation of the automotive stability control. As indicated in FIG. 2, the CVT Automotive Stability System  10  then returns from Step  32  to Step  30 , whereupon if Step  30  detects that the Automotive Stability Computer  12  is not actively engaged (no), the CVT Automotive Stability System  10  goes to a Step  36 . In Step  36  the CVT Automotive Stability System  10  determines whether the Electronic Transmission Control  14  and CVT  20  are in a State  38  wherein the actual current ratio conforms to a set or strategy ratio, that is, a normal ratio. If the CVT Automotive Stability System  10  is in State  38 , the CVT Automotive Stability System  10  proceeds to Step  26 . If the CVT Automotive Stability System  10  is in State  38  (yes), the CVT Automotive Stability System  10  returns to the start of Step  26 . When the actual ratio diverges from the set ratio or strategy ratio (normal ratio) (no), the CVT Automotive Stability System  10  enters a Transition Function Step  40  and a Transition Function  42  ensues, which provides a comfortable passage to the “normal ratio”, whereupon the CVT Automotive Stability System  10  returns to the start of Step  26 . 
     According to the invention, the transition function is a function of the vehicle speed (v_Fzg) and variables equivalent to the driving speed such as the output rotational speed (n_AB), the existing actual ratio (i_V_ist) and the divergence thereof from the new set ratio of the normal driving strategy (i−_V). 
     In the CVT tip function with rigid gear steps, a ratio change stopped by the “freezing” of the variator ratio is resumed. In a CVT tip function with variable or sliding gear ratios, the “frozen” ratio value serves, according to the invention, as the basis for calculation of additional gear ratios. 
     As added variants within the scope of this invention, the method described can be implemented in a separate driving strategy computer or directly in the automotive stability control unit or other adequate control units.