Abstract:
A method is described for control of a CVT automatic transmission ( 1 ) in which a sensed main pressure (p_hd_act) and a sensed contact pressure (p_s 2 _act) of a secondary pulley ( 7 ) are entered as signals in an electronic transmission control ( 8 ). For diagnosis of an error in the sensing of the main pressure (p_hd_act) and/or of the contact pressure (p_s 2 _act) of the secondary pulley ( 7 ) their actual values or comparison variable (|p_hd_act-p_hd_nom|, |p_s 2 _act-p_s 2 _nom|) formed therefrom are compared with applicable threshold values (p_hd_min, pd_phd_regdiff, p_s 2 _min, pd_ps 2 _regdiff) associated with a range of plausible pressure values.

Description:
According to the type defined in more detail in the preamble of Claim  1 , the invention concerns a method of controlling a CVT automatic transmission in which an electronic transmission control comprises a main pressure and a contact pressure of a secondary pulley. 
     Modern automatic transmissions work with an electronic transmission control (EGS) by means of which can be met criteria relevant to information an safety. The electronic transmission control which as a rule communicates with an engine control unit from the transmission motor and side of the vehicle. From the input signal and stored data such as gear shift characteristic lines for gears, tuning parameters for pressure calculation, engine engagement and time steps, the same as regulators and diagnosis parameters, the electronic transmission control calculates the correct gear and optimum pressure curves for gear shifts by means of adequate program modules. 
     To ensure a correct operation of the automatic transmission, great importance is attached to the reliability of the input signals, since otherwise there is chosen a shifting program not adapted to the operation situation which under circumstances can result in damage to the transmission and dangerous situation in the operation. 
     In CVT automatic transmissions, together with the rotational speeds of the primary pulley and secondary pulley of the variator, the main pressure and the contact pressure of the secondary pulley which is decisive for the variator&#39;s capability of torque transmission, especially constitute important input variables on which the correctness of the transmission control essentially depends. 
     DE 196 50 218 A1 discloses a method for monitoring the orderly operation of two rotational speed sensors associated with the primary and secondary cone pulley pairs wherein brief failure of the rotation speeds can also be detected and react thereto with adequate flexibility. This is obtained by the fact that in the presence of a stationary state during travel, a ratio of the variator is determined from the rotational speed signals of the primary and secondary pulleys and the ratio is coordinated with a first characteristic field, the characteristic field having a range of admissible and a range of non-admissible ratios. An error is detected when the ratio is in a non-admissible range and with the detection of the error the contact pressure level of the variator is raised in a first step and if the presence of the error persists, an emergency drive program is activated in a second step. 
     While with the method known already, a monitoring of the signals delivered by the rotational speed sensors is possible, the verification of the signals issued by the pressure sensors to the electronic transmission control is unsatisfactory. 
     In the practice, two sensors are provided for pressure monitoring, namely, one sensor after a main-pressure supply pump and one sensor on the secondary pulley or hydraulic chamber thereof. 
     When the sensors or the current regulators thereof are defective, erroneous pressure values are issued. The same applies when a failure occurs in the pressure preparation, e.g. in case of a mechanical defect in the transmission. Even though in that case, the pressure values can lie outside a tolerance range, the sensing of the electronic transmission control is not detected as defect so that an incorrect adaption is effected in that case. 
     The problem, on which this invention is based, is to make available a method for control of a CVT automatic transmission in which an electronic transmission control comprises a main pressure and a contact pressure of a secondary pulley, the pressure values being verified as to plausibility. 
     SUMMARY OF THE INVENTION 
     The inventive method offers the advantage that in the sensing of the main pressure and of the contact pressure of the secondary pulley of the variator failures can be reliably detected so that further processing of non-plausible pressure values can be prevented. 
     Since for reasons of consumption an objective of the control of the CVT automatic transmission consists in keeping the pressure level as high as needed but as low as possible, the inventive method makes it possible to implement a transmission control optimated in terms of consumption and with which is prevented a pressure availability too high on account of an error in the pressure sensing. 
     Besides, it is possible with the inventive method advantageously to ensure that seriously erroneous pressure values cannot lead to any control of the CVT automatic transmission that can damage the automatic transmission or impair the stability of the vehicle. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     Other advantages and developments of the invention result from the embodiments described in principle herebelow with reference to the drawings. In the drawings: 
     FIG. 1 is a simplified system diagram of a CVT automatic transmission; 
     FIG. 2 is a flow chart of a program module for parallel testing of a sensed main pressure and of a sensed secondary pulley pressure; 
     FIG. 3 is a flow chart of one other program module for serial testing of the sensed pressures with parallel monitoring and adaption of the pressures; and 
     FIG. 4 is a flow chart of one other program module for serial testing of the sensed pressures with parallel monitoring of an adaptation of the pressures. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to FIG. 1, it shows an extensively simplified diagram of a CVT automatic transmission of a design known per se such as has been described in ATZ Automobiltechnische Zeitschrift  96  (1994), page 380. Here can be seen a variator  2  having situated on the input side a cone pulley pair  3 , a belt-drive organ  4  and a second cone pulley pair  5  situated on the output side. Both the primary cone pulley pair  3  and the secondary cone pulley pair  5  consist of a primary pulley  6  stationary in axial direction and a secondary pulley  7  movable in axial direction by pressure actuation. The running radius of the belt-drive organ  4  and, therefore, also the ratio is determined by the axial position of the movable primary pulley  6  or secondary pulley  7 , respectively. 
     An electronic transmission control (EGS)  8  having an electronic control unit  9  receives signals, among others, from a selector lever  10 , a rotational speed sensor  11  of primary pulley  6 , a rotational speed sensor  12  of secondary pulley  7 , a main pressure sensor  13 , a secondary pulley pressure sensor  14  and other signal transmitters symbolically shown with an arrow  15 . The electronic control unit  9  determines from the input variables operation parameters of the automatic transmission  1  such as a ratio, an operating point and a pressure level in the primary and secondary pulleys. 
     The sensors  13 ,  14  for detecting a main pressure p_shd and a contact pressure p_ss 2  on the secondary pulley, which pressures determine the contact between belt-drive organ  4  and secondary cone pulley pair  5  and thus the capability for torque transmission of the system, constitute a unit with the electromagnetic pressure regulators. The pressure of the pressure regulators  13  and  14  is supplied by a main pressure delivery pump  16  which conveys the hydraulic medium from an oil sump  7  via a filter  18 . 
     The pressure values issued by the pressure sensors  13 ,  14  to the electronic transmission control  9  are tested for plausibility by means of a program module in the electronic control unit  9 . 
     To this end, two different inquiries are made in which are tested for each pressure sensed a nominal-actual pressure difference |p_hd_act-p hd_nom| or |p_s 2 _act-p_s 2 _nom| and an adaptation or regulation with which it is sought to equate the actual pressure and the nominal pressure. 
     FIG. 2 to FIG. 4 show each a flow chart of a program module for monitoring the pressure sensory analysis of the CVT automatic transmission  1 , wherein are carried out in FIG. 2 a parallel test of the sensed pressure, namely, of the contact pressure p_s 2 _act on the secondary pulley  7  and of the main pressure p_hd_act, in FIG. 3 a serial test of the sensed pressures and in FIG. 4, a serial test for plausibility of the sensed pressures with parallel monitoring of the adaptation in the electronic transmission control  8 . 
     At the beginning, in each program module is verified in a function F 1  whether the automatic transmission is ready for operation, i.e. that an ignition has been engaged, that the engine speed has been self-adjusted after starting the engine and that the oil pressures in the transmission have reached a height which ensures sufficient operation of the transmission. As long as no readiness for operation is detected, it is tested, starting from a minimum engine rotational speed n_mot_min  1 , whether a minimum pressure level p_hd_min and p_s 2 _min have at all been reached on both pressure branches. 
     Otherwise, it is assumed that a defect exist in the oil supply. If the transmission is not ready to operate and thus sufficient oil supply is not ensured, the automatic transmission still is not ready to move. Thus no verification for plausibility of the sensed pressures has significance. 
     When in the F 1  function, no readiness for operation of the automatic transmission is detected, in a program part A is checked whether there has been a regular pressure buildup after start of the motor. 
     For this purpose in a function F 2  is tested whether the motor rotational speed n_mot is higher than an applicable threshold value for a minimum motor rotational speed n_mot_min  1 . 
     When the result of the inquiry in the function F 2  is negative, i.e. the motor rotational speed n_mot is below the minimum value for the motion of the motor starting from which, in spite of correct transmission operation, no oil pressure can build up, the diagnosis is discontinued and a function F 3  is activated for abandoning (exit) the diagnosis. 
     Simultaneously, a position information diag_tree_p=0 is issued. With each possible exit from the program is associated one such position information with which the actual position in the program module can be monitored on an adequate indicator. In this way can easily be established which inquiry has precisely been carried out in the program module. 
     Since in different possibilities of exit from the program module, the function to abandon (exit) or one and the same error notice is possible, the position information allows the precise coordination of an exit or error information with an inquiry so that the event that has occurred can be exactly diagnosed and an error with its position can be stored in the error memory. The position information in addition simplifies the adjustment and analysis of the existing function or condition thereof. 
     When in the function F 2  is detected that the motor rotational speed n_mot is higher than the threshold n_mot_min  1 , in a function F 4  is tested whether the sensed main pressure p_hd_act is higher than a threshold value p_hd_min associated there with and the contact pressure p_s 2 _act on the secondary pulley  7  is higher than the threshold value p_s 2 _min associated therewith. 
     When the result of the inquiry of the function F 4  delivers that the sensed pressures p_hd_act and p_s 2 _act are higher than the respective threshold values, an “exit” function F 5  to abandon the diagnosis is activated on a position diag_tree p=2. Otherwise, that is, when at least one of the sensed pressures p_hd_act and p_s 2 _act is below the threshold value associated therewith, in a function F 6  is issued an error “error  1 ” associated with this situation in which the main pressure p_shd has not correctly built up at the start of the motor, and the error with the position information diag_tree_p=1 is stored in the error memory. 
     When returning to the program module of FIG. 2 for function F 1  and the development of the method is observed for the case that in the function F 1  a readiness for operation of the automatic transmission has been detected, there follows in this embodiment a parallel inquiry of the sensed pressures p hd act and p_s 2 _act. To this end, a program part B is branched off to for inquiry of the contact pressure p_s 2 _act on the secondary pulley and the program part C is branched off to for inquiry of the main pressure p_hd_act. 
     If the program part B is first observed for inquiry of contact pressure p_s 2 _act, in a function F 7  there is monitored, during applicable time t_ps 2 _regdiff which constitutes a local filtering time, the nominal-actual pressure difference |p_s 2 _act-p_s 2 _nom| on the secondary pulley  7  to see whether it exceeds an applicable threshold value of pressure differences pd_ps 2 _regdiff, which at present amounts to  6  bar. When the function F 7  delivers the result that the nominal-actual pressure differences |p_s 2 _act-p_s 2 _nom| on the secondary pulley  7  is not lower than the threshold value pd_ps 2 _regdiff, in a subsequent function F 8  a defined error notice “error  2 ” is issued in the program module for an error in the pressure sensing on the secondary pulley  7 , here for too great a pressure difference on a position diag_tree_p=3. 
     When the nominal-actual pressure difference |p_s 2 _act-p_s 2 _nom| on the secondary pulley  7  still is admissible, it is tested in a function F 9  whether a pressure adaptation or regulation for equating the actual pressure p_s 2 _act with the nominal pressure p_s 2 _nom of the secondary pulley is active. If this not the case, the diagnosis tree is exited from in a subsequent function F 10  and the program module is abandoned in a position diag_tree_p=4. 
     When, like in the instant case, a pressure adaptation or pressure regulation has been provided and in the function F 9  is detected as active, it is tested in another function F 11  whether the pressure adaptation or regulation has reached in an applicable time t_s 2 _reglimit a defined upper adaptation or regulation limit s 2 _reglimit_pos or a lower adaptation or regulation limit s 2 _reglimit_neg. 
     The pressure adaptation is conducted via a current i_s 2  passed to the pressure regulator  14  of the secondary pulley  7 . The intensity of the current is associated via a characteristic line with a required pressure on the pressure regulator  14 . Here is provided an offset band surrounding the characteristic line of +/−50 mA in this case, which is limited by the upper adaptation or regulation limit s 2 _reglimit_pos and the lower adaptation or regulation limit s 2 _reglimit_neg. Within the offset band changes of intensity of the current are admissible for adapting the current. 
     For equation of the actual pressure p_s 2 _act or p_hd_act with the appertaining nominal pressure p_s 2 _nom or p_hd_nom, both an adaptation and a regulation are conceivable. 
     When neither the upper nor the lower adaptation limits are detected as having been reached, in one other “exit” function F 12  the program module is abandoned on a position diag_tree_p=5. 
     However, in case the upper or the lower adaptation or regulation limit has been reached, in a function F 13  the error notice “error  2 ” is issued for too great a pressure difference on the secondary pulley  7  and recorded in the error memory with a position diag_tree_p=6. 
     Similarly to the program part B for inquiring the contact pressure p_s 2 _act is configurated the program part C for inquiring the main pressure p_hd_act which runs parallel therewith. 
     Thus, in a function F 14 , during an applicable local filtering time t_phd_regdiff, the nominal-actual pressure difference |p_hd_act-p_hd_nom| of the main pressure is first examined as to whether it exceeds an applicable threshold value of pressure difference pd_phd_regdiff. When the result delivered by the function F 14  is that the nominal-actual pressure difference |p_hd_act-p_hd_nom| of the main pressure is not lower than the threshold value pd_phd_regdiff, in a subsequent function F 15  a defined error notice “error  3 ” on a position diag_tree_p=7 is issued for an error in the pressure sensing of the main pressure, here for too great a pressure difference, and recorded in the error memory. 
     When the nominal-actual pressure difference |p_hd_act-p_hd_nom| of the main pressure still is admissible, in a function F 16  is tested whether a pressure adaptation or regulation for equating the actual pressure p_hd_act with the nominal pressure p_hd_nom of the main pressure supply is active. If this is not the case, in a subsequent function F 17  the diagnosis tree is abandoned and the program module left on a position diag_tree_p=8. 
     In case a pressure adaptation or regulation has been detected in the function F 16  as active, in another function F 18  is tested whether the pressure adaptation or regulation has reached, in an applicable time t_hd_reglimit, a predetermined upper adaptation or regulation limit hd_reglimit_pos or lower adaptation or regulation limit hd_reglimit_neg. The adaptation limit, in turn, form here an upper and lower edge of an offset band around a characteristic line in which a current intensity is stored for control of the main pressure regulator  13  depending on a required main pressure. 
     When neither the upper nor the lower adaptation or regulation limit is detected as having been reached, i.e. the variation of the current of the pressure regulator  13  for the main pressure p_shd moves within the offset band or within the regulation limits, in another “exit” function F 19 , the program module is left on a position diag_tree_p=9, returning here, the same as in every other exit, from the program module back to the beginning thereof. 
     However, if the upper or the lower adaptation or regulation limit hd_regdiff_pos or hd_reglimit_neg is reached, in a function F 20  the error notice “error  3 ” is issued for too great a pressure difference of the sensed main pressure and is retained in the error memory with a position diag_tree_p=10 so that it can be verified with the aid of an error printout that there is an error in the pressure sensing of the main pressure on account of an adaptation or regulation limit having been reached. 
     In FIG. 3 is shown a program module for monitoring the pressure sensory analysis in which for the case that the transmission is not ready to operate a program part A is run through like in FIG.  2 . But when in the function F 1  a readiness to operate of the transmission has been detected, then follows here a serial inquiry of the sensed pressures p_hd_act and p_s 2 _nom, there being first tested for plausibility the sensed main pressure p_hd_act in a program part C′ and, optionally thereafter, the sensed contact pressure p_s 2 _act on the secondary pulley in a program part B′. 
     With the prioritization of the main pressure p_hd_act, it is advantageously taken into account that the contact pressure p_s 2 _act on the secondary pulley  7  depends on the supply with the main pressure p_hd_act so that an eventual detection of error in the sensing of the main pressure p_hd_act is taken into account when examining the contact pressure p_s 2 _act on the secondary pulley. 
     For the sake of clarity, the position information is provided with an apostrophe in the program module of FIG.  3 . 
     When in the function F 1  a readiness for operation of the automatic transmission is detected, in a subsequent function F 21  is inquired whether the error “error  3 ”, i.e. an error in the sensing of the main pressure p_hd_act, had already been detected in a previous run through of the program and stored in the error memory. 
     In case of negative result of the inquiry, i.e. no error “error  3 ” has been stored in the error memory, the main pressure in the program part C′ is inquired. The construction of the program part C′ essentially corresponds to that of the program part C in FIG.  2 . 
     At the same time in a function F 22  corresponding to the function F 14  in FIG. 2, during the applicable time t_phd_regdiff, the nominal-actual pressure difference |p_hd_act-p_hd_nom| of the main pressure is first examined as to whether it is less than the applicable threshold value of pressure difference pd_phd_regdiff. In case of negative result of the inquiry, in a subsequent function F 23 , the error notice “error  3 ” provided for an error in the pressure sensing of the main pressure is issued with a position information diag_tree_p=3′ and is recorded in the error memory. 
     When the nominal-actual pressure difference |p_hd_act-p_hd_nom| of the main pressure is still admissible, in a function F 24  is tested whether a pressure adaptation or regulation is active. If this is not the case, the program part B′ is branched off to for inquiring the contact pressure p_s 2 _act on the secondary pulley. 
     In case a pressure adaptation or regulation is detected as active in the function F 24 , it is tested in another function F 25  corresponding to the function F 18  in FIG. 2 whether the pressure adaptation or regulation, in an applied time t_hd_reglimit has reached the upper adaptation limit hd_reglimit_pos or the lower adaptation or regulation limit hd_reglimit_neg. 
     If it is found that the adaptation or regulation occurs within the limits, the program part B′ is branched off to for inquiry of the contact pressure p_s 2 _act on the secondary pulley. But if the upper or the lower adaptation or regulation limit hd_reglimit_pos or hd_reglimit_neg has been reached, then in a function F 26  the error notice “error  3 ” is issued and retained in the error memory with a position indication diag_tree_p=4. 
     When the result delivered to the inquiry in the function F 21  is that an error already exists in the sensing of the main pressure p_hd_act in the error memory, without inquiring the main pressure p_hd_act the program part B′ is directly branched off to for inquiry of the contact pressure p_s 2 _act on the secondary pulley, a substitute function F 27  being first activated. This defines that the main pressure p_hd_act is correct, a sensor defect being accordingly assumed. 
     Thereafter is started the program part B′ which in its construction essentially corresponds to the program part B in FIG.  2 . Thus, in a function F 27  corresponding to the function F 7  in FIG. 2, it is first tested during a filtering time t_phd_regdiff whether the nominal-actual pressure difference |p_s 2 _act-p_s 2 _nom| on the secondary pulley is lower than the applicable threshold value of pressure difference pd_ps 2 _regdiff. In case of negative result of the inquiry, in a subsequent function F 28 , the error notice “error  2 ”, defined for an error in the pressure sensing of the secondary pulley on a position diag_tree_p=5′, is issued and recorded in the error memory. 
     If the nominal-actual pressure difference |p_s 2 _act-p_s 2 _nom| on the secondary pulley still is admissible, in a function F 29  is inquired whether a pressure adaptation or regulation is active. If this is not the case, in a subsequent function F 30  the program module is abandoned on a position diag_tree_p=6′. In case a pressure adaptation or regulation has been detected as active, it is tested in another function F 31  corresponding to the function F 11  in FIG. 2 whether the pressure adaptation or regulation, in the applicable time t_s 2 _reglimit, has reached its upper adaptation or regulation limit s 2 _reglimit_pos or its lower adaptation or regulation limit s 2 _reglimit_neg. 
     When the variation of the current of the pressure regulator  14  for the secondary pulley pressure p_s 2 _act moves within the adaptation or regulation limits, the program module is abandoned in an “exit” function F 32  on a position diag_tree p=7′, returning back to its beginning. But if the upper or the lower adaptation or regulation limit, respectively s 2 _reglimit_pos or s 2 _reglimit_neg, is reached, then in a function F 33  the error notice “error  2 ” is issued for too great a pressure difference of the sensed secondary pulley pressure and retained in the error memory with a position diag_tree_p=8′. 
     FIG. 4 shows one other program module for monitoring the pressure analysis wherein, after ascertaining in the function F 1  that the automatic transmission is ready for operation, parallel with the inquiry of the sensed main pressure p_hd_act and of the contact pressure p_s 2 _act on the secondary pulley regarding the observance of the respectively admissible actual-nominal pressure difference, the monitoring of the adaptation or regulation limits for the adaptation or regulation of the pressures is carried out. 
     In this manner a very advantageous saving of time can be obtained when running through the program module. The working off of the program module according to FIG. 4 also proves itself to be particularly quick since, as in the embodiment of FIG. 3, a prioritization of the inquiry of the main pressure p_hd_act has been effected. Thus, an unnecessary working off of the program part for monitoring the secondary pulley pressure p_s 2 _act in case of a main pressure problem can be omitted or, when error has already been detected in the sensing of the main pressure p_hd_act, it can be ensured by a delay time that the secondary pressure p_s 2 _act be again enquired only when a substitute function for the main pressure p_hd_act has stabilized and thus an error detection in the secondary pulley pressure p_s 2 _act resulting from a main pressure error can be ruled out. 
     The sequence of the program module in FIG. 4 shows that in automatic transmissions not ready for operation like in the embodiments of FIG.  2  and FIG. 3, the program part A is passed through. But when readiness for operation is detected, first the sensed main pressure p_hd_act in a program part C″ and, if necessary thereafter, the sensed contact pressure p_s 2 _act on the secondary pulley in a program part B″ are tested for plausibility. 
     For the sake of clarity, the position information in the program module of FIG. 4 is provided with a double apostrophe. 
     As is seen in FIG. 4, in the program part C″ is tested, for inquiry regarding a main pressure error in a function F 34  corresponding to the function F 24  in FIG. 3, whether a pressure adaptation or regulation is active. In case of negative result of the inquiry, in a function F 35  is issued a status S 1  leading to the abandonment of the program module and in case of positive result of the inquiry, in a function F 36  is inquired whether the local filtering time t_hd_reglimit has reached the upper adaptation or regulation limit hd_reglimit_pos or the lower adaptation or regulation limit hd_reglimit_neg. Insofar as the adaptation or regulation is longer than the filtering time t_hd_reglimit on one of the stops mentioned, in a function F 37  a status S 2  is set which leads to an error detection. But when the adaptation or regulation during the filtering time t_hd_reglimit has been carried out within the adaptation or regulation limits, a status S 3  is issued in a function F 38 . 
     Parallel with this, in a function F 39  is inquired whether the nominal main pressure p_hd_nom lies between a lower detection limit ps_hddet_min and an upper detection limit ps_hddet_max of the main pressure sensor  13 . 
     Since the main pressure sensor  13  detects only the value of the detection limit, which in the upper can here amount, e.g. to 40 bar, as long as the real main pressure is above or below the detection limits, there already results in an existing nominal main pressure p_hd_nom a nominal-actual pressure difference so that the diagnosis must be cut off when exceeding or falling below the detection limits. For this case a status S 4  is issued in a subsequent function F 40 . 
     When the nominal main pressure p_hd_nom is between the detection limits of the main pressure sensor  13 , in another function F 41  corresponding to the function F 22  in FIG. 3, an inquiry is started as to whether during the local filtering time t_phd_regdiff the nominal-actual pressure difference p_hd_act-p_hd_nom of the main pressure lies within the applicable threshold value of pressure difference pd_phd_regdiff. 
     Insofar as the threshold value of pressure difference pd_phd_regdiff is exceeded longer than the filtering time t_phd_regdiff, in a function F 42  is set a status S 6  leading to an error notice. Otherwise, when the threshold value of the pressure difference pd_phd_regdiff has not been exceeded, a status S 5  is issued in a function F 43 . 
     In a function F 44  for inquiring the status, the status information of the functions F 35  to F 38  and F 40  to F 43  are compared. 
     When the status S 2  and S 4  are present, i.e. an adaptation or regulation limit and the detection limit of the main pressure sensor have been exceeded, or when status S 2  and S 5  are present, i.e. an adaptation or regulation limit has been exceeded and the threshold value of the pressure difference pd_phd_regdiff has not been exceeded, the error notice “error  3 ” is issued in a function F 45  with a position information diag_tree_p=3″. 
     In case the status S 6  and S 1  are present, i.e. the threshold value of pressure difference pd_phd_regdiff has been exceeded and no pressure adaptation or regulation has been detected as active, or when status S 6  and S 3  are present, i.e. the threshold value of the pressure difference pd_phd_regdiff has been exceeded and the adaptation or regulation during the filtering time t_hd_reglimit has been carried out within the adaptation or regulation limit, the error notice “error  3 ” with a position diag_tree_p=4″ is retained in a function F 46 . 
     When the status S 2  and S 6  are present, i.e. one of the adaptation or regulation limits and the threshold value of the pressure difference pd_phd_regdiff have been exceeded, then the error notice “error  3 ” with a position information diag-tree_p=5″ is recorded in the error memory in a function F 47 . 
     When on the contrary status S 1  and S 4  are present, i.e. no pressure adaptation or regulation has been detected as active and the detection limit of the main pressure sensor has been exceeded, an “exit” function F 48  for leaving the program module is activated in a position diag_tree_p=6″, since a branching off to inquire the secondary pulley pressure is not important. 
     When in a function F 49  on a position diag_tree_p=7″, it is detected that status S 5  and S 3  are present, i.e. the threshold value of the pressure difference pd_phd_regdiff and the adaptation or regulation limits have not been exceeded, or that status S 1  and S 5  are present, i.e. no pressure adaptation or regulation is active and the threshold value of the pressure difference pd_phd_regdiff has not been exceeded, then the sensing of the main pressure is detected as being in order. After assurance of the main pressure readiness, the program module B″ can be started to inquire the secondary pulley pressure. 
     The transition from the program part C″ for monitoring the main pressure sensing to the program part B″ for monitoring the pressure sensing of the secondary pulley, after diagnosis of an error and appearance of the error notice “error  3 ” in one of the functions F 45 , F 46 , F 47  is delayed in a subsequent function F 50  by a delay time t_delay to ensure the building up of a substitute function for the main pressure p_shd. 
     The possibility, when monitoring the secondary pulley pressure sensing in the program part B″, of a sequence of errors resulting from lack of readiness of the main pressure is therewith prevented. The delay time t_delay is to be applied and it amounts to 1000 ms in this case. 
     With the start of the substitute function, the pressure value delivered by the main pressure sensor is ignored, since it is not plausible. Instead of this, the main pressure is purely controlled without adaptation or regulation, the control being carried out according to a predefined characteristic line loaded with a safety offset in which a current intensity of the pressure regulator is associated with a nominal main pressure. 
     As soon as the substitute function is started, the delay time begins to run. When the substitute function is reset, i.e. when the detected error no longer exists, the delay time is also reset. 
     When the function F 50  delivers the result that the delay time has elapsed, the program part B″, which is essentially configurated like the program part C″, is branched off to for monitoring the sensing of the secondary pulley pressure. 
     At the same time, in a function F 51  is first tested whether a pressure adaptation or regulation is active. If the result of the inquiry is negative, in a function F 52  a status S 3 ′ is issued and if the result is positive, in a function F 53  is inquired whether during the local filtering time t_s 2 _reglimit the upper adaptation or regulation limit s 2 _reglimit_pos or the lower adaptation limit s 2 _reglimit_neg has been reached. When the latter is the case, in a function F 54  a status S 1 ′ is set which leads to an error detection. But if the adaptation or regulation during the filtering time t_s 2 _reglimit remains within the adaptation or regulation limits, a status s 2 ′ is issued in a function F 55 . 
     Parallel herewith in a function F 56  is inquired whether the nominal contact pressure p_s 2 _nom on the secondary pulley  7  lies between a lower detection limit ps_s 2 det_min and an upper detection limit ps_s 2 det_max of the secondary pulley pressure sensor. If the result of the inquiry is negative, i.e. the detection limits have been exceeded or fallen below, the diagnosis is discontinued and a status  84 ′ is issued in a subsequent function F 57 . 
     When the nominal contact pressure p_s 2 _nom on the secondary pulley is between the detection limits of the secondary pulley pressure sensor, in another function F 58  is inquired whether during the local filtering time t_ps 2 _regdiff the actual-nominal pressure difference lies within the applicable threshold value of the pressure difference pd_ps 2 _regdiff. 
     If the result of the inquiry is negative, i.e. the threshold value of the pressure difference pd_ps 2 _regdiff has been exceeded during the filtering time t_ps 2 _regdiff, in a function F 59  is set a status S 6 ′ leading to an error notice. Otherwise, when the threshold value of the pressure difference pd_ps 2 _regdiff has not been exceeded, a status S 5 ′ is issued in a function F 60 . 
     The status issuances of the functions F 52 , F 54 , F 55  and F 57  to F 60  are issued to a function F 61  for status inquiry and are there compared. 
     When status S 1 ′ and S 4 ′ are present, i.e. an adaptation or regulation limit and the detection limit of the sensor of the secondary pulley pressure have been exceeded, or when status S 1 ′ and S 5 ′ are present, i.e. an adaptation or regulation limit have been exceeded and the threshold value of the pressure difference pd_ps 2 _regdiff has not been exceeded, the error notice “error  2 ” is issued with the position information diag_tree_p=10″ in a function F 62 . 
     In case the status S 6 ′ and S 2 ′ are present, i.e. the threshold value of the pressure difference pd_ps 2 _regdiff has been exceeded and the adaptation or regulation has been carried out within the adaptation or regulation limits, or when status S 6 ′ and S 3 ′ are present, i.e. an inadmissible nominal-actual pressure difference and no pressure adaptation or regulation have been detected, the error notice “error  2 ” is retained with a position information diag_tree_p=11″ in a function F 63 . 
     When status S 1 ′ and S 6 ′ are present, i.e. an adaptation or regulation limit and the threshold value of the pressure difference pd_ps 2 _regdiff have been exceeded, the error notice “error  2 ” is likewise recorded in the error memory with a position information diag_tree_p=12″ in a function F 64 . 
     If on the contrary status S 3 ′ and S 4 ′ are present, i.e. no pressure adaptation or regulation has been detected and the detection limit of the sensor of the secondary pulley pressure has been exceeded, an “exit” function F 65  for leaving the program module is activated on a position diag_tree_p=14″, returning back to the beginning of the program module. 
     When in a function F 66  is detected in a position diag_tree_p=15″ that status S 3 ′ and S 2 ′ are present, i.e. no pressure adaptation or regulation is active and thus also no adaptation or regulation limit has been exceeded, or that status S 2 ′ and S 5 ′ are present, i.e. the adaptation or regulation limit and the threshold value of pressure difference pd_ps 2 _regdiff has not been exceeded, or that status S 3 ′ and S 5 ′ are present, i.e. no pressure adaptation or regulation is active and the threshold value of pressure difference pd_ps 2 _regdiff has not been exceeded, the pressure sensing of the contact pressure on the secondary pulley is detected as being in order and the beginning of the program module is returned to. 
     Thus it is concluded that the pressure value sensed is not plausible whenever one of the errors “error  1 ”, “error  2 ”, “error  3 ” has been detected. A reaction to this can be that the pressure adaptation or regulation be deactivated to prevent that the erroneous adaptation or regulation and an actual-nominal pressure difference possibly be further increased. After deactivation of the pressure adaptation or regulation, the pressure regulator is purely operated, the controlled pressure being loaded with an additional safety value. 
     In these embodiments, it has been provided that in case of an error detection in the pressure sensing, such as the detection of an inadmissible ratio, the contact pressure level of the variator is increased with reference to rotational speeds of the cone pulley pairs  3 ,  4  by an added program module of the electronic transmission control  8  and if the error persists that an emergency drive program be activated in another step. 
     In embodiments differing from these, other adequate consequences can obviously be drawn from the error detection in the pressure sensing. 
     Reference numerals 
       1  cvt automatic transmission 
       2  variator 
       3  primary cone pulley pair 
       4  belt-drive organ 
       5  secondary cone pulley pair 
       6  primary pulley 
       7  secondary pulley 
       8  electronic transmission control (EGS) 
       9  electronic control unit 
       10  selector lever 
       11  rotational speed sensor 
       12  rotational speed sensor 
       13  main pressure sensor, pressure regulator 
       14  secondary pulley pressure sensor, pressure regulator 
       15  signal transmitter 
       16  main pressure delivery pump 
       17  oil sump 
       18  filter 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 A, A′, A″ 
                 program part for monitoring a pressure buildup 
               
               
                 B, B′, B″ 
                 program part for monitoring the secondary 
               
               
                   
                 pulley pressure 
               
               
                 C, C′, C″ 
                 program part for monitoring the main pressure 
               
               
                 diag_tree_p 
                 position information 
               
               
                 error 1 
                 error in buildup of the main pressure 
               
               
                 error 2 
                 error in the pressure sensing of the secondary 
               
               
                   
                 pulley pressure 
               
               
                 error 3 
                 error in the pressure sensing of the main 
               
               
                   
                 pressure 
               
               
                 F 
                 function 
               
               
                 hd_reglimit_neg 
                 lower adaptation or regulation limit for 
               
               
                   
                 adaptation or regulation of the main pressure 
               
               
                 hd_reglimit_pos 
                 upper adaptation or regulation limit for 
               
               
                   
                 adaptation or regulation of the main pressure 
               
               
                 n_mot 
                 rotational speed of the motor 
               
               
                 n_mot_min1 
                 applicable threshold value for static 
               
               
                   
                 rotational speed of the motor 
               
               
                 p_hd_act 
                 sensed main pressure 
               
               
                 p_hd_min 
                 threshold value for the main pressure 
               
               
                 p_hd_nom 
                 nominal value for the main pressure 
               
               
                 |p_hd_act-p_hd_nom| 
                 nominal-actual pressure difference of the 
               
               
                   
                 main pressure 
               
               
                 p_s2_act 
                 sensed contact pressure on the secondary 
               
               
                   
                 pulley, secondary pulley pressure 
               
               
                 p_s2_min 
                 threshold value for secondary pulley pressure 
               
               
                 p_s2_nom 
                 nominal value for secondary pulley pressure 
               
               
                 |p_s2_act-p_s2_nom| 
                 nominal-actual pressure differences of the 
               
               
                   
                 secondary pulley pressure 
               
               
                 pd_phd_regdiff 
                 applicable threshold value of pressure 
               
               
                   
                 difference 
               
               
                 pd_ps2_regdiff 
                 applicable threshold value of pressure 
               
               
                   
                 difference 
               
               
                 ps_hddet_max 
                 upper detection limit of the main pressure 
               
               
                   
                 sensor 
               
               
                 ps_hddet_min 
                 lower detection limit of the main pressure 
               
               
                   
                 sensor 
               
               
                 ps_s2det_max 
                 upper detection limit of the secondary pulley 
               
               
                   
                 pressure sensor 
               
               
                 ps_s2det_min 
                 lower detection limit of the secondary pulley 
               
               
                   
                 pressure sensor 
               
               
                 S 
                 status 
               
               
                 s2_reglimit_neg 
                 lower adaptation or regulation limit for 
               
               
                   
                 adaptation or regulation of the secondary 
               
               
                   
                 pulley pressure 
               
               
                 s2_reglimit_pos 
                 upper adaptation or regulation limit for 
               
               
                   
                 adaptation or regulation of the secondary 
               
               
                   
                 pulley pressure 
               
               
                 t_hd_reglimit 
                 applicable time 
               
               
                 t_phd_regdiff 
                 applicable local filtering time 
               
               
                 t_ps2_regdiff 
                 applicable local filtering time 
               
               
                 t_s2_reglimit 
                 applicable time 
               
               
                 t_delay 
                 delay time for buildup of a substitute function 
               
               
                   
                 for the main pressure