[001] METHOD FOR DETERMINING THE MASS OF A yOTOR. VEHICLE [004] The invention concerns a method for determining Ihe mass of a motor vehicle, which is implemented in combination with a shift of an autonic tic variable-speed transmission from a current gear to a desired gear, sucii thai ii determine a mass value, force and movement parameters are determined parily before or after the shift and partly during the shift. [005] [006] Knowledge of the mass of a motor vehicle Is of elementary irriportance in order to enable optimum control of the shifting behavior of an automated transmission. Thus, the mass is needed for calculating the driving resistance, accurate determination of which is required for determining the shift speed at which the current gear, currently engaged, should be changed by a shift operation, and for determining the desired gear to which the transmission should be changed by the shift. For example, in the case of commercial vehicles whose mass can change markedly as a result of loading and unloading, the mass cf the motor vehicle is also needed for determining the starting gear. [007] From EP 0 695 930 A1, a method for determining the mass or total weight of a motor vehicle Is known. This known method relates to a motor vehicle whose drive train comprises an internal combustion engine provided with an electronic control system as the drive engine and a manual shift transmission. To determine the total weight of the motor vehicle, it Is provided that at each of time points related to an upshift process, the torque of the drive engine and the longitudinal acceleration of the motor vehicle are determined, and the vehicle weight is calculated therefrom. The first values are preferably determined immediately before the engine clutch Is engaged and the engine torque increased and the second values after the engine clutch has been completely engaged and the engine torque has been increased. To improve the accuracy of the total weight so determined, an average of several weight values is formed, each calculated from the same first values and from second values determined at various times. However, since in particular the time point when the first, values are dolermined is chosen unfavorably because of the engaged synchronization and the e ngagemenf of the desired gear, the weight value so determined is relatively inaccurate. f008] Another method for determining the mass of a motor vehicte is the object of WO 00/11439. This method relates to a motor vehicles with an automated shift transmission 'n which the traction force is interrupted during a gearshift. The method provides that within a time window immediately before or after the gearshift several traction force values, i.e., force magnitudes, and in vhe traction-force-free phase during the shift operation at least two speed values, and accordingly movement magnitudes, are determined and a mass value is calculated from these. Since the mass value determined by this method can also be comparatively inaccurate, it is provided to form an average value from several mass values determined during a driving cycle. [009| A disadvantage of both known methods, apart from the inaccuracy of the weight or mass values determined, is also the fact that only one mass value can be determined at each shift operation so that to form an average value relatively many gearshifts and a correspondingly longer driving cycle time are "equired. [010] Thus, the purpose of the present invention is to propose a method whereby the mass of a motor vehicle can be determined more rapidly and with greater accuracy than has hitherto been possible. [011] [012] To achieve this objective the invention starts from a method for determining the mass of a motor vehicle, which is implemented in combination with a shifting operation of an automated transmission from a current gear to a desired target gear, such that to Determine a mass value, force and movement parameters are determined partly before or after, and partly during the shift operation. [013] This method also provides that the drive-wheel-related traction force of the drive engine is determined before and after the shift as F_zug_vor and F_zug„nach, and the longitudinal acceleration of the motor vehicle is determined before and after the shift as a_zug_vor and a_zug_nach and also, in Ihe traction-force-free phase (rolling phase) during the shift, the acceleration a_roll during the roiling phase is determined, and from these In accordance with the formula m = F„2ug /( a_2ug - a_rolf) a first mass value m_vor = F_zug_vor / (a_z.ug_vor ~ a_ro!!) is calculated for the beginning of the shift operation and a scjcond mass value m_nach = F_zug_nach / (a_2ug_nach - a_jcM) is calculated for the end of the shift operation. [014] According to the generaiiy accepted driving resistance equation: the traction force F__zug of the drive engine related to the drive wheels of the motor vehicle is a function of the driving resistance F_fw, which consists of the sum of the road inclination resistance F__steig, the rolling resistance F_ro!i and the air resistance FJuft, and of the mass inertia! force F_trag of the motor veiicle. Since the mass inertia! force F_ trag is the product of the current mass m o' the vehicle and the current acceleration a of the vehicle in accordance with F_ trag = m*a, the driving resistance F__fw can be written in the form: F_fw = F_zug - m*a [015] If it Is assumed that the driving resistance F_fw does iiot change substantially immediately before, during and immediately after a shitt operation, and because the drive train is disengaged in the traction-force-free phase of the shift (F_zug_roll = 0), the following relationships are obtained: F_fw_vor = F_zug_vor - m*a_zug_vor = F_fw_rol! = -m*a_rol! and F_fw_roll = -m*a_roll = F_fw_nach = F_zug_nach ~ m*a_zug_na(:h [016] From the above, in each case for two mass values per shift operation: [017] Thus, by way of the method, in each case, two mass values per shift operation are determined, the first mass value m^vor being associated in time with the beginning of the shift operation and the second mass value mi_nach with the end thereof. The accuracy of the two mass values m_vor, m__nach is rejlated to the respective time of determining the traction force values and acceleration values and the specific procedure during this and is, at the very least, no worse than the accuracy of the weight or mass values determined by the known methods. [018] As regards accuracy, the determination of the acceleration a_rQl! during the traction-force-free phase of the shift operation between the disengaging and engaging of the engine clutch is particularly critical, since in this phase substantially unknown forces or torques, which can only be measured with difficulty, can act upon the output side of the drive train. For example it is largely unknown how quickly the torque of the drive engine decreases and increases again during a shift operation, what fraction of the torque Is lost due to the synchronization of the target area, and how rotation fluctuations, which can be set going by the shift process, such as by the disengaging and engaging of the engine clutch, by the disengagement of the load gear and the synchronization and engagement of the target area, or by unevenness of the road, affect the driving dynamic of the motor vehicle, i.e., the acceleration of the motor vehicle at the time. [019] Accordingly, it is provided that the acceleration a_roll during the rolling phase of the shift is preferably determined in such a manner that over a time interval At, which includes the traction-force-free phase of the sfiift, several discrete values a_i of the current acceleration a of the motor vehicle are determined, from these acceleration values aj the minimum acceleration a_min is determined in the case of a traction shift and the maximum acceleretion a_max is determined in the case of a thrust shift, and this extreme value of the acceleration (a_min or a___max) is then used as the acceleration scroll in the traction-force-free roliing phase. [020] Experience has shown that using this procedure, trie acceieraion a_rall is determined with process reiiability and high accuracy so that the mass values m___vor and m_nach derived therefrom are thus also determined relatively accurately. [021] To improve accuracy when determining the acceleration s_rol! in the traction-force-free pha.5e and hence the measured vaiiiss m_vor and m jiach, it is expedient to determine the acceieration values aj for determining an optimum extreme value (a_min or a_max) at intervals of at most 10 ms. In tiis respect, it is a!so advantageous, in order to eliminate measurement errors and faults in the determination of the extreme value of the acceleration (a_min or a_niax), for the acceleration values aJ to be filtered, and for doing this generally known numerical methods are available. [022] However, since the mass values m_vor and m_nach, detarmined as described earlier for an individual shift process, may be too inaccurata for control purposes such as determining the shift speed and the target gegr for future shifts in each case, it is expedient to average the mass values mj determined over several shift operations. Specifically for this, it is provided that after the determination of mass values has started, those mass values mJ which satisfy predetermined minimum conditions are summed fortheformation of a first average mass value m_m1 provided for control purposes, until a predetermined minimum number n of mass values mJ have been reached, and then the first average mass value m_m1 is calculated by mathematical averaging using the formula m_m1 = 1/n*ImJ, (i = 1, n) and this average mass value m_m1 is first used for control purposes. [023] A minimum condition can be that the acceleration difference a_zug - a_ro(l is larger than a predetermined lower limit value Aa_min of the acceleration difference (a_zug - a_roll > Aa_min). Another minimum condition (;an be that, during a traction shift, the traction force F__zug is larger than a predetermined lower limit F_Zmin of the traction force (F_zug > F_Zmin), and during a thrust shift smaiier than a predetermined upper firnit value F_Srriax of the Hirust force (F_zug < F_Smax) [024] Practica! tests have shown that the minimum number n of masn values mj required for the dettirrninalion of a sufficiency accurate average rnsss vaiue m_rri 1, is of the order of 10 to 20 values. [025] in this manrier, therefore, in a relatively short; time, i.e., undcjr favorable conditions already after 5 shifts, a reiativeiy accurate ftrst average mass vafue m__ m1 is determined, which can then be used for contro! purpcses, [026] Until this first average mass value mjnl is available, it is expediently provided that a default mass value m_Def, for example an average tsetween the unloaded mass and the maximum permissible overall mass, or an estimated mass value m_Sch, which can be the average mass last determined during the previous driving cycle, is used for control purposes. [027j To determine a more accurate average mass value, it is advantageously provided that after the minimum number n of mass values mJ has been reached and the first average mass value m_m1 has been calculated, additional mass values mJ are determined which satisfy predetermined conditions for good mass values m_gutj, and the first average mass value m_m1 is corrected ujiing the said additional good mass values m__gutj. [028] This correction could be effected by the successive replacement of the poor mass values m_schlechtj used for the first average mass value m__m1 by the additionally determined good mass values m_gut_!. Disadvantageous y, however, this would involve elaborate indexing of the poor mass values m_sctilechtj and overall greater computational effort. [029] Accordingly, in the present context, a procedure for the correctiCfn of the first average mass value m_m1 is favored, in which already during the summing of the mass values mJ to form the first average mass value m_m1 those mass values mJ which do not satisfy the conditions for good mass values £ re summed to form a poor-value sum Im_schlecht_i (1 = 1, n_sch(echt), the additional good mass values m_gut_i are determined and summed to form a good-value sum Im_gutJ {i = 1, n_gut) until their number n_gut is the seme as the number n_schlecht of the previously summed poor mass values m._schiechtj. and then, by replacing the poor-value sum Im__schiechtJ with the good-value sum Im jutj in the overall sum ImJ of mass values mj, a more e F__zug__Zmin1) in the case of a traction shift and in the case of a thrust shift smaller than a predetermined limit value F_zug_Smax1 (F_zug_vor < F_zug_Sma)c1). [033] in addition, t can be provided that a condition for good mass values at the end of the shift operation m_nach_gut is that the road inclinatiori difference between the initiation of the shift, a_vor, and the calculation of the sescond mass value, a_nach, should be smaller than a predetermined limit value A_max2 ( i a_vor - a_nach i < A a_max2). [034] A further condition for good mass values at the end of the shift m_nach_gut is that the traction force at the time when the second mass value m_nach is calculated, in the case of a traction shift, should be larger than a predetermined limit value F__zug_Zmin2 (Fzug__nach > F_zug_Zmin2) and in the case of a thrust shift smaller than a predetermined limit value F__zug_Smax2 (F_zug_vor < F_zug_Smax2). [035] In addition, a condition for good mass values at the end of the shift operation m_nach_gut is that the torque difference of the drive engine, before and [038] Particuiarly Am__m_max or \ m_mg! - m_m2 | > Am_m_max). [040] [041] To clarify the invention the description of a drawing is attac;hed, which shows: [042] FIG. 1 is a flow chart of the method according to the invention; [043] FIG. 2 is a measured time variation of the vehicle's acceleration a over several traction shifts, and [044] FiG. 3 is a simplified time variations of the traction force F_;:ug and the acceieration a for a single traction upshift. |046j The flow chart of FIG.. 1 ifiustrates the sequence in time of » method in simplified form. When the motor vehicle begins operating, the process of determining the mass of the motor vehicle is started; and after initiaiization in step S1, in step S2 during starting a first, relatively inaccurate mass value is determined. In a next step S3 tv»/o respective mass values are determined over a shift operation. In step S4, any already present mass values are sunmed and a first average mass value m_m1 is calculated from them. In a next step S5, those mass values mj, which do not satisfy the conditions for good mass values and are, therefore, classified as poor, are summed to give a poor-value sum Im_schiechtJ. [047] Then, in a step S6, it is checked whether the necessary minimum number n of mass values mJ for forming the first average mass value m_m1 has already been reached. If not, steps S3 to S6 are repeated until the minimum number n of mass values mJ is reached. [048] After this, in a step S7, the first average mass value m_m1 is stored as an initializing value for future driving cycles. In a next step S8, additionally determined mass values m_gutj classified as good values are summed. [049] Then in a step S9, it is checi Aa_min). 7. The method according to claims 5 or 6, characterized in that a minimum condition is that the traction force F_zug in a traction shift should be larger than a predetermined lower limit value F___Zmin of the traction force (F_zug > F__Zmin) and in a thrust shift it should be smaller than a predetermined upper limit value F_Smax of the thrust force (F___zug < F__Smax). 8. The method according to at least one of claims 5 to 7, characterized in that the minimum number n of mass values m J is of the order of 10 lo 20 values. 9. The method according to at least one of claims 5 to 8, cha-acterized in that before the minimum number n of mass values mJ has beer reached, a default mass value m_Def or an estimated mass value m_Sch is used for control purposes. 10. The method according to at least one of claims 5 to 9, characterized in that when the minimum number n of mass values m J has been reached and the first average mass vaiue m_m1 has been calculated, additional mas;; values mj are determined which satisfy predetermined conditions for good mass values m_gutj, and the first average mass value m_m1 is corrected t»y taking into account the said additional good mass values m_gutj, 11. The method according to claim 10, characterized in that the correction of the first average mass value m_m1 is carried out in such manner that already during the summing of the mass values mJ to form the said first average mass value m_m1, those mass values mJ which do not satisfy the conditions for good mass values are summed to give a poor-value sum Im_schlechtJ (i = 1, n_schlecht), the additional good mass values m_gutj are determined and summed to give a good-value sum Im_gulJ (i ^ 1, n^gut), until their number ri_gut is equal to the number n_schlecht of the previously summed poor mass values m__schlecht J, and then, by replacing the poor~\/afue sum Im_£:chlechy by the good-value sum Im_gutJ in the overall sum Imj of the first ax'erage mass value m___m1, a more exact, second average mass value m_m2 is caici iiated, which is thereafter used for control purposes. 12. The method according to claims 10 or 11, characterized in that a condition for good mass values m_vor gut at the beginning of the stsift operation is that the road inclination difference between the initiation of the shift a_vor and the rolling phase a_roll should be smaller than a predetermined limit value Aa_max1 (| a__vor - a_roll | < Aa_max1). 13. The method according to at least one of claims 10 to 12, characterized in that a condition for good mass values m_vor_gut at the beginning of the shift operation is that the traction force F_zug_vor before the shift should be larger than a predetermined limit value F__zug_Zmin1 (F_zug_vor > F_zug_„Zmin I) in the case of a traction shift, and smaller than a predetermined limit value F_zug_Smax1 (F__zug__vor < F_zug_SmaKl) in the case of a thrust shift. 14. The method according to at least one of claims 10 to 13, c haracterized in that a condition for good mass values m_nach__gut at the end of the shift is that the road inclination difference between the initiation of the shift a _vor and the calculation of the second mass value a_nach should be smaller than a predetermined limit value Aa_max2 (| a_vor- a_nach j < Aa_max2). 15. The method according to at least one of claims 10 to 14, characterized in that a condition for good mass values m_nach_gut at the end of tfie shift is that the traction force at the time when the second mass value m_nach is calculated should be larger than a predetermined limit value F__zug_Zmin2 (F_zug_nach > F_zug_Zmin2) in the case of a traction shift and smaller than a predei:ermined limit value F_zug_Smax2 (F_zug_vor < F_zug_Smax2) in the case of a thrust shift. 16. The method according to at least one of claims 10 to 15, characterized in that a condition for good mass values m_nach_gut at the end of the shift is that the torque difference of the drive engine before and after the shift, M_zug„vor, 18. The method according to at ieast one of claims 10 to 17, criaracterized in that a condition for good mass values m_vor_gul, m_nach_gut is that the gear {load gear G__L) engaged before the shift should be higher thein a lowest gear G__m!n and lower than a highest gear G_max (G_L > G_min, G__ < G_max). 19. The method according to at least one of claims 5 to 18, ciiaracterized in that a change of the vehicle's mass m compared with the current a\'erage mass value (m__m1 or m__m2) is determined, and if a predetermined change limit value m_max is exceeded, the determination of a new average mass veilue (m_m1, m_m2) is started. 20. The method according to claim 19, characterized in that a sliding average value m_mgl is calculated continuously from mass values mj which satisfy the conditions for good mass values m_vor_gut, m__nach_gut, and the determination of new average mass values m_m1, m_m2 is started if the difference between the sliding average mass values m_mgl and the last- determined average mass value (m_m1 or m_m2) exceeds a predetermined limit value Am_m_max ( | m_mgl - m_m1 | > Zim_m_max or | m__mc)l - m_m2 ] > Am_m_max).