A method for determining a torque transfer between wheels of the same axle in low speed conditions

Abstract

There is described a method for determining a torque transfer between wheels of the same axle of a motor vehicle, comprising: - acquiring, for each wheel of the axle, at least one of a value of the internal pressure of a tyre of the wheel (TP_FR, TP_FL, TP_RR, TP_RL) and a value of travel of a suspension associated with the wheel (ST_FR, ST_FR, ST_RR, ST_RL), - determining, on the basis of said at least one of a value of an internal pressure of a tyre of the wheel (TP_FR, TP_FL, TP_RR, TP_RL) and a value of travel of a suspension associated with the wheel (ST_FR, ST_FR, ST_RR, ST_RL), a value of load acting on each wheel of the axle, - determining a difference between the values of the loads acting on the wheels of the axle (D24R, D24F), and - determining a value of a locking torque for the axle (32R, 32F) as a function of said difference between the values of the loads acting on the wheels of the axle.

Description

[0001] A method for determining a torque transfer between wheels of the same axle in low speed conditions

[0002] TEXT OF THE DESCRIPTION

[0003] Field of the Invention

[0004] The present invention refers to electronic systems for a variable torque distribution in motor vehicles.

[0005] Known Art

[0006] The variable torque distribution in the driveline of a motor vehicle (so-called "torque vectoring") is a significant part of the control strategies available on board a vehicle, and it may concern either the needs of a single axle - i.e., a variable distribution from right to left in the same axle - or the needs of a four-wheel drive, wherein the distribution may also vary between different axles. The present invention concerns the distribution within a single axle.

[0007] The torque vectoring may be performed either by purely mechanical devices (typically, limited slip differentials which in case may be locked) , or by means of electronically controlled devices, which are the concern of the present invention. The latter type includes electronically controlled differentials (electronic limited slip differential or self-locking differential) , conventional friction brakes, as well as electric drive motors.

[0008] More specifically, the existing strategies for torque vectoring generate commands to differentials and / or friction brakes which are based on vehicle accelerations measured by on-board sensors, according to an estimate of the wheels grip and to the speed of the wheels .

[0009] At high vehicle speeds it is possible to control such devices in pre-emptively, with the purpose of correcting the vehicle trajectory or modifying the propensity to oversteer or understeer. On the other hand, at low vehicle speeds, especially in extreme off-road conditions (such as, e.g., in a so-called rock crawling drive) , the torque vectoring strategy has the only aim of maximizing the traction on the wheels having high grip. In such circumstances, the accelerations of the vehicle mainly represent the inclination of the vehicle, and therefore the control is mainly reactive: when a significant difference in speed is detected between the left wheel and the right wheel, the devices are controlled in such a way that both wheels have the same speed, and therefore the amount of torque necessary to propel the vehicle is sent to the wheel having the maximum grip.

[0010] The reactive operation, however, implies the introduction of delays in the driveline, because it requires the occurrence of an initial slip event of the wheels on the individual axle, and therefore requires a difference in speed of the wheels. This leads to a temporary absence of propulsion from the whole axle, which is compensated only when the reactive control logic starts acting in order to limit the difference in speed between the wheels, and therefore only when a difference in speed is detected between the wheels of the axle. Obviously, this is all but desirable in a low-speed manoeuvre, because it can lead to unacceptably long intervention times.

[0011] Object of the Invention

[0012] The present invention aims at solving the technical problems outlined in the foregoing. Specifically, the invention aims at providing a method for the pre-emptive determination of a torque transfer between the wheels of an axle at low speeds of the vehicle, and therefore for a determination before the event which requires the torque transfer. Summary of the Invention

[0013] The obj ect of the invention is achieved by means of a method having the features provided in the claims that follow, which form an integral part of the technical disclosure provided herein with reference to the invention .

[0014] Brief Description of the Figures

[0015] The invention will now be described with reference to the annexed Figures , provided as non-limiting examples only, wherein :

[0016] - Figure 1 shows an exemplary block diagram of a method according to the invention;

[0017] Figures 2 and 3 show exemplary block diagrams of elements of the method of the diagram as per Figure 1 , and

[0018] Figure 4 shows an exemplary block diagram of an integration of a processing unit , implementing the method according to the invention, within the vehicle .

[0019] The text matter provided in the Figures in addition to the references aims at supporting the description, without necessarily constituting a limitation thereof . Detailed Description

[0020] Reference 1 in Figure 1 generally denotes a block diagram of a method for determining a torque trans fer between wheels of a same axle of a motor vehicle according to the invention .

[0021] As a general introduction, and anticipating the detailed description of the individual steps which will be provided in the following, the method according to the invention comprises , in the embodiments thereof :

[0022] - acquiring, for each wheel of the axle , at least one of a value of the internal pressure of a tyre of the wheel ( i . e . an inflation pressure ) and a value of travel of a suspension associated with the wheel ,

[0023] - determining, on the basis of said at least one of a value of an internal pressure of a tyre of the wheel and a value of travel of a suspension associated with the wheel , a value of load acting on each wheel of the axle ,

[0024] - determining a di f ference between the values of the loads acting on the wheels of the axle , and

[0025] - determining a value of a locking torque for the axle as a function of said di f ference between the values of the loads acting on the wheels of the axle .

[0026] In the diagram of Figure 1 , which represents the method 1 according to the invention, it is possible to distinguish four logic units of the method . Speci fically, reference 2 and reference 4 identify two nested logic units , of which reference 2 denotes a logic unit adapted to manage - pre-emptively and reactively - the torque trans fer between wheels of a same ( front or rear ) axle at low speeds . Reference 6 denotes a logic unit adapted to determine the torque distribution between the front axle and the rear axle , and it is shown in a rectangle in dotted lines , meaning that it is a logic unit outside the scope of the invention, the obj ect whereof is limited to one axle . Reference 8 denotes a logic unit corresponding to the reactive management of the torque trans fer between wheels of the same axle ; this is also shown as a rectangle in dotted lines , meaning that it is a logic unit outside the scope o f the invention . The units 4 and 8 are both nested within unit 2 , according to what has been described in the foregoing .

[0027] The blocks 10F, 10R represent the determination of the values of the locking torque , respectively for the front axle and the rear axle, as a function of the di f ference between the values of the load acting on the wheels of the axle .

[0028] Upstream of blocks 10F, 10R the input takes place of the data concerning the pressure of the tyres , which are associated with reference TP, and concerning the travel of the suspensions ST. Based on the characteristics of the vehicle, there may be present either both input data, or only one of them. Typically, it is possible to envisage embodiments wherein the input data only comprise the item of data TP, and embodiments wherein the input data contain both data TP and ST, particularly when the vehicle is equipped with pneumatic suspensions, or generally speaking active suspensions, configured for monitoring (and controlling) the travel.

[0029] The data TP and / or ST are fed to a block 12, which comprises one or more control states o cycles, which check the plausibility of the input data before transmitting them to a (frequency) filter stage shown as block 14. The block 14 generates two output items of data, one for each axle: an output 16F, corresponding to the data TP and / or ST for the front axle, which are subjected to plausibility check and filtering, and an output 16R corresponding to the data TP and / or ST for the rear axle, which are subjected to plausibility check and filtering. The data 16F, 16R are fed to the blocks 10F, 10R in combination with other data, including: data 18F (front axle) , 18R (rear axle) , representing meeting an enabling condition at the application of locking torques to the corresponding axle

[0030] - data 20F, 20R, representing values of the target torque to be delivered respectively through the front axle (20F) and the rear axle (20R) . As can be seen in Figure 1, the data 20F, 20R come from the logic unit 6, and are the result of determining the torque distribution between the front axle and the rear axle; data 22F (front axle) , 22R (rear axle) , respectively corresponding to an external request of deactivation of the torque transfer (i.e., of inhibition of the method according to the invention) on the front axle and on the rear axle . I f the deactivation request is applied on one axle , the method according to the invention is not implemented on that axle .

[0031] The data 16F, 16R are directly processed by calculation and deduction stages internal to blocks 10F, 10R, the data 18 F, 20F, 22 F and 18R, 20R, 22R substantially defining boundary conditions .

[0032] Initially, the data 16F, 16R are first processed in order to determine , based on at least one item of the data TP, ST - respectively corresponding to a value of the internal pressure of a tyre of the wheel and to a value of travel of a suspension as sociated with the wheel

[0033] - a value of load acting on each wheel of the axle . The value of load acting on each wheel of the axle is a value of vertical load .

[0034] It is to be noted that the data TP, ST are twofold, because they refer to the right side and to the left side . Based on the load acting on each wheel of the axle , within each block 10F, 10R a determination is made of a di f ference D24_F, D24_R between the values of the loads acting on the wheels of the front axle and of the rear axle , respectively . Once the values D24_F, D24_R are determined, a locking torque is determined by means of the deductions as per blocks 26F, 26R, which determine

[0035] - on the basis of the data D24_F, D24_R - a locking torque for the front axle 28 F and a locking torque for the rear axle 28R . The locking torques 28 F, 28R are determined particularly on the bases of the values of the target torque 20F, 20R, coming from logic unit 6 .

[0036] The locking torques 28R, 28 F converge into a combination block 30 which also receives the output data of the reactive logic unit 8 , speci fically reactive locking torques FT ( front axle ) and RT ( rear axle ) which are determined, inter alia, on the basis of the speed of the wheels WS . The block 30 combines , as a function of the travel conditions of the vehicle , the torques which have been pre-emptively calculated by means of the logic unit 4 and the torques which have been reactively calculated by means of the logic unit 8 , therefore determining final values of the locking torques 32 F ( front axle ) and 32R ( rear axle ) . The locking torques 32 F, 32R are used as input data for controlling locking actuators ( schematically represented as block ACT , in dotted lines because the management thereof is not a direct obj ect of the invention) and moreover for an interface block 34 which suggests to the vehicle driver possible blocking actions which may be implemented manually through the devices on board the vehicle ( item of data 36 ) and through the status thereof ( item of data 38 ) .

[0037] With reference to Figure 2 , it shows a detailed block diagram corresponding to the blocks 10F, 10R, therefore to the level of the logic unit 4 - calculation of the locking torques at low speeds . Figure 2 represents the calculation performed on the individual axle , and the calculation proceeds in the same way for the front axle and for the rear axle .

[0038] The input data comprise :

[0039] - the travel of a left suspension ST_L and the travel of a right suspension ST_R,

[0040] - the inflation pressure of a left tyre TP_L and the inflation pressure of a right tyre TP_R,

[0041] - the bias of the value of the inflation pressure on the front axle TP_BF or the bias of the value of the inflation pressure on the rear axle TP_BR,

[0042] - the target torque for the axle 20F, 20R,

[0043] - an estimated value of grip G_EST .

[0044] The data ST_L, ST_R and TP_L, TP_R are provided as input to the block 10F, 10R in a filtered form, the detail whereof is represented in the following Figure 3 . The first data (ST_L, ST_R) are converted into dimensionless values, in order to limit the interval of the following calibration of the calculation models. The second data (TP_L, TP_R) have no bias, because the starting values of the inflation pressure of the tyres may not be symmetrical on the axle of interest.

[0045] As regards the bias, the phenomenon must be considered from an operational perspective. The values of the inflation pressure of the tyres of one axle may not be symmetrical due to (more or less marked) differences of the mass of air introduced into the tyres. Moreover, the difference in the inflation pressure may be due to the interaction between the tyre and the ground, e.g. to the deformation due to travelling on rocks or on uneven ground (which is a frequent condition for an off-road vehicle) . For the calculation, it is advisable to eliminate the part of the difference due to phenomena other than the one being investigated: in other words, it is necessary to eliminate - by means of a compensation - the difference due to the inflation only (i.e. the bias) . This is clearly visible in Figure 2: at block 40, the values TP_L and TP_R are subtracted, thereby obtaining an unbiased pressure difference DTP_B, from which there is subtracted - for compensation (block 42) - a value of the difference in inflation pressure TP_BL (left) , TP_BR (right) which is only due to inflation differences and not to the interaction with the ground, thereby obtaining a biased value of the difference in inflation pressure DTP.

[0046] The biased value DTP is sent to a block 44, which extracts from it the absolute value, which in turn becomes an input variable for a one-dimensional map LUT_DP (so-called "ID look-up table") wherein the values of load difference between the wheels of the same axle are provided as a function of the biased values DTP. It shall be borne in mind, however, that if the filtering logic determines that the bias is not reliable (BNR) , for the following calculations a predefined value will be resorted to. This is exemplified by a switch block SW1 with two outputs, the former (OFF) corresponding to a situation of reliable bias, and outputting the previously calculated value DLT, the latter (ON) corresponding to a situation of non-reliable bias (BNR) and outputting a value of predefined difference in load DVF_P .

[0047] As regards the calculation procedure concerning the data ST_L, ST_R, the latter are subjected to normalization in a block 46 which outputs percentual values (generally speaking, all forms of normalization are possible) STP_L (left) , STP_R (right) , which are sent to respective blocks LUT_L and LUT_R, corresponding to one-dimensional maps wherein the values of the (vertical) load acting on the wheel are provided as a function of the percentual (or normalized) values of the travel of the suspensions, while taking into account the typically non-linear behaviour of the suspensions.

[0048] The values STP_L (left) , STP_R (right) are also used as input data for a plausibility check which involves the difference thereof and the difference DTP. From the two differences (STP_L - STP_R and DTP) the sign is extracted (blocks SI for STP_L - STP_R and S2 for DTP) for a comparison in a block S_D. The block S_D outputs a signal with the logic state "0" if the signs of both differences STP_L - STP_R and DTP are the same, while it has the logic state "1" if the signs of the two differences STP_L - STP_R and DTP are different. In the latter case, i.e., if the load difference between the wheels of the same axle does not comply with the sign of the difference in inflation pressure (and vice versa) , an error signal DPL_ERR (plausibility error) is generated. The error signal DLP-ERR is the result of an AND logical operation (block Al) between the signal output from block S_D and the logical negation of the signal BNR. This is due to the fact that the coherence check of the signs of the differences STP_L - STP_R and DTP is applicable only when the difference DTP is reliable, and therefore when the bias is reliable. In the presence of a non-reliable bias (logic state BNR = "1") , it is possible to detect non-coherent signs, and therefore a difference DTP which is not coherent with the difference STP_L - STP_R.

[0049] However, it shall be borne in mind that plausibility errors (i.e. non-coherent signs of the differences STP_L - STP_R and DTP) may occur also if a tyre is very inflated but it is detached from the ground - which is all but unlikely while travelling off-road. In this case, the signs of the two differences are probably different, but the bias may be reliable. If the deduction were not mediated with the item of data BNR, the result would be a false deduction of implausibility, or anyway an underestimate of the necessity of an intervention.

[0050] Taking into account the truth table of the AND operator in block Al, and assuming that a signal of plausibility error DLP_ERR corresponds to a logic value "1" output from block Al ("1" when the error exists, otherwise "0" when the error does not exist and the determinations are plausible) , while a value of the item of data BNR corresponding to a non-reliable bias is associated with a logic value "1" of the same item of data, the operator of block Al outputs an indication of implausibility DLP_ERR = "1" in the case a) , i.e. noncoherent signs (logic output of block S_ID = "1") and reliable bias (value BNR = "0", but being input into block Al as a logical negation, therefore as "1") >> output DLP_ERR = "1". In all the remaining cases, specifically: b) coherent signs (logic output of block S_ID = "0") and non-reliable bias (value BNR = "1", but being input into block Al as a logical negation, therefore as "0") » output DLP_ERR = "0" c) non-coherent signs (logic output of block S_ID = "1") and non-reliable bias (value BNR = "1", but being input into block Al as a logical negation, therefore as "0") » output DLP_ERR = "0" d) coherent signs (logic output of block S_ID = "0") and reliable bias (value BNR = "0", but being input into block Al as a logical negation, therefore as "1") , therefore as "0") >> output DLP_ERR = "0".

[0051] Such logic meets the need of distinguishing a condition of non-coherent signs, which generally indicates a reduced reliability of all the consequent deductions, from a non-reliable bias condition, which has a lesser gravity than the condition of non-coherent signs .

[0052] As regards the diagnostics management, DLP_ERR is defined as a "punctual" error, it being the result of monitoring without filters and without the storage or error codes, or without corrective actions. It essentially corresponds to an indicator of a potential problem.

[0053] For the purposes of diagnostics, the punctual error may be associated to an error code to be stored, downstream of the filtering operations and, especially, a correction path may be added (in this case employing the data 18F, 18R) , according to the configuration of the vehicle and to the boundary conditions of the error. More generally: if the signs are coherent and the bias is reliable, no punctual error is present, and it is possible to calculate the locking torque in a pre-emptive fashion .

[0054] - if the signs are non-coherent and the bias is reliable, the condition will be signalled by DLP_ERR = "1", through subsequent diagnosis activities, by means of which it will be possible to determine corrective actions (logic deactivation, 0 Nm pre-emptive locking torque, only possible reactive actions, etc.) ; this is the case described in the foregoing, with a fully inflated tyre which however is raised from the ground.

[0055] - if the bias is non-reliable, irrespective of the sign coherence, the condition may be read for the purpose of a diagnosis for a possible storage of error codes, but no functional deactivation is necessary because the block SW1 anyway ensures a neutralization of the branch managing the processing based on the inflation pressures of the tyres.

[0056] The values of the (vertical) load output from blocks LUT_L and LUT_R are subjected to a subtraction operation in a block 48, and from the resulting difference an absolute value DLS is extracted in a block 50. Moreover, the values of the (vertical) load output from blocks LUT_L and LUT_R are subjected to a minimum operation in a block 52, which outputs a value of minimum vertical load acting on the wheels of the axle (the minimum between the loads acting on the two wheels) , which is represented by a block 54 and associated to the letter A. The minimum load 54 is moreover an input item of data for calculating the torque transmissible by the wheel subjected to the lesser load. Specifically, the value 54 is multiplied by the factor G_EST and converted into a torque information at block 56. The output of block 56, which corresponds to the torque transmissible by the wheel subjected to the lesser load, is denoted as 58 (letter B) , and is moreover an input item of data for a block HYS which takes into account hysteresis phenomena within the differential (non-biased torque within the differential, which provides a minimum effect of non- symmetrical distribution) . The inputs of block HYS comprise the torque 58, a value of inner losses H, and a reference value amounting to half the target torque 20F, 20R for the front axle and the rear axle, respectively. The latter value is obtained by extracting the absolute value of data 20F, 20R (block 59A) , and by halving the absolute value (block 59B) .

[0057] The value DLS and the output of the switch block SW1 are compared in a block MAX_D, which outputs the value of maximum load difference between the wheels of the same axle, corresponding to the item of data D24F for the front axle and D34R for the rear axle. The data D24F, D24R are then used as a first input item of data for a bi-dimensional map LUT_DL (so-called "2D look-up table) . The halved value of the target torque 20F, 20R is used to compose a second item of data input into map LUT_DL, specifically a difference (block 60) between the value 58 of the torque transmissible by the wheel subjected to the lesser load and the halved value of the target torque 20F, 20R itself. From the result of such difference there is extracted the absolute value (block 62) , and the latter defines the second item of data input into the map LUT_DL . The output value corresponds to a target locking torque based on the load difference, and it is sent to a second switch module SW2, which determines a preliminary value 28F* 28R* of the locking torque requested for the front (F) or the rear (R) axle. The control variable for the switch module SW2 is the output of block HYS: if the value 58 of the torque transmissible by the wheel subjected to the lesser load is higher than the halved value of the target torque, then the preliminary value 28F* 28R* of the locking torque requested for the front (F) or the rear (R) axle is zero (0 Nm, block 63) . The reason is simple: if the torque transmissible by the less loaded wheel - i.e. half of the maximum torque transmissible by the differential - equals the halved value of the target torque, then the axle is perfectly able to transmit the target torque, event taking into account the internal losses H. On the other hand, the torque 28F*, 28L* corresponds to the output of the bi-dimensional map LUT_DL, and it is sent to a combination module MIO, which guarantees the emission of an output signal (and therefore of a value of the torque) irrespective of the upstream logical operations.

[0058] In any case, if the enabling conditions (data 18F, 18R) are not met, a predefined value of the locking torque is generated, which amounts to 0 Nm, and is sent to block MIO, or else, if the enabling conditions are met, the preliminary torque 28F*, 28R* - resulting from the calculation - is generated. In other words, block MIO prevents the data output by means of the method according to the invention from corresponding to an indeterminate value or to an indeterminate state.

[0059] With reference to Figure 3, this Figure schematically shows the detail of the filter block 14. The input data comprise the values of the travel of the suspensions and of the tyre inflation pressure for each wheel of the vehicle, specifically:

[0060] - a value of the travel of a front right suspension ST_FR,

[0061] - a value of the travel of a front left suspension ST_FL,

[0062] - a value of the travel of a rear right suspension ST_RR,

[0063] - a value of the travel of a rear left suspension ST_RL, a value of the inflation pressure of a tyre of a front right wheel TP_FR,

[0064] - a value of the inflation pressure of a tyre of a front left wheel TP_FL,

[0065] - a value of the inflation pressure of a tyre of a rear right wheel TP_RR,

[0066] - a value of the inflation pressure of a tyre of a rear left wheel TP_RL .

[0067] Such values are filtered, preferably by means of a low-pass filter, according to the ( front-rear ) axle of the vehicle , with the following set of filters : a low-pass filter LP_ST_F for the suspension travel data on the front axle , a low-pass filter LP_ST_R for the suspension travel data on the rear axle , a low-pass filter LP_TP_F for the inflation pressure data on the front axle , a low-pass filter LP_TP_R for the inflation pressure data on the rear axle .

[0068] A block 64 calculates a right-left di f ference between the filtered signals output from the filters LP_TP_F and LP_TP_R, thereby obtaining raw data about the di f ference of the non-biased inflation pressure TP_BF* and TP_BR* for the front axle and for the rear axle . These data form one of the inputs to a third switch module SW3 , the control variable whereof is a status indication concerning the bias calculation, exempl i fied in block BRW .

[0069] The precondition is that the calculation of the bias on the inflation pressure must take place when the vehicle is in a quiet condition, characteri zed by a low speed, reduced slope of the ground / low lateral acceleration, reduced di f ference of travel of the suspensions . Therefore , the bias determination window exempli fied by the block BRW comprises three logic states BRI , BR2 , BR3 . The state BRI corresponds to a condition of closing the calculation window due to a failure to meet the conditions concerning the vehicle . More speci fically, in the state BRI at least one ( OR) of the following relations is true :

[0070] Vehicle speed >= ThrOFF_spd

[0071] Grade >= ThrOFF_grd

[0072] LatAccel >= ThrOFF_LatAcc SuspTravelDi f f >= ThrOFF_susp

[0073] Wherein :

[0074] - Vehicle speed is the speed of the vehicle ,

[0075] - ThrOFF_spd is a deactivation threshold for the calculation window BRW, expressed as a function of the vehicle speed,

[0076] - Grade is the slope of the ground,

[0077] - ThrOFF_grd is a deactivation threshold for the calculation window BRW, expressed as a function of the slope of the ground, - LatAccel is the lateral acceleration of the vehicle ,

[0078] - ThrOFF_LatAcc is a deactivation threshold for the calculation window BRW, expressed as a function of the lateral acceleration,

[0079] - SuspTravelDi f f is a di f ference in travel of the suspensions of the vehicle ,

[0080] - ThrOFF_susp is a deactivation threshold for the calculation window BRW expressed as a function of the di f ference in travel of the suspensions .

[0081] The logic state BR2 is the opposite of the logic state BRI , and it corresponds to a condition of bias calculation on the inflation pressure . Speci fically, in the state BR2 at least one ( OR) of the fol lowing relations is true :

[0082] Vehicle speed < ThrOFF_spd OR Grade < ThrON_grd OR

[0083] LatAccel < ThrON_LatAcc OR SuspTravelDif f < ThrON_susp

[0084] Wherein :

[0085] ThrON_spd is an activation threshold for the calculation window BRW, expressed as a function of the vehicle speed, ThrON_grd is an activation threshold for the calculation window BRW, expressed as a function of the slope of the ground, ThrON_LatAcc is an activation threshold for the calculation window BRW, expressed as a function of the lateral acceleration, ThrON_susp is an activation threshold for the calculation window BRW, expressed as a function of the di f ference in travel of the suspensions .

[0086] The passage from the logic state BRI to the logic state BR2 is substantially determined by exceeding ( in either direction) the thresholds mentioned in the foregoing .

[0087] The logic state BR3 , which is accessible only from the logic state BRI , corresponds to a condition of implausibility of the bias , due to the acquisition of non-coherent data . Speci fically, the logic state BR3 is brought about when a rapid change of the inflation pressure takes place when the vehicle is substantially still , therefore when both (AND) the following conditions are true :

[0088] Vehicle speed = 0

[0089] Tyre press change rate >= ThrIMPL_prschng

[0090] Wherein :

[0091] Tyre press change rate is a change rate of the inflation pressure of the tyres ThrIMPL_prschng is an implausibility threshold expressed as a function of the change rate of the tyre pressure . In operational terms , in such a condition the value of the bias on the di f ference in inflation pressure must be ignored, because it derives from interventions on the vehicle which are not part of the normal conditions , speci fically a tyre deflation when the vehicle is still in extremely challenging of f-road conditions .

[0092] The return to the state BRI takes place when both conditions determining the passage to the state BR3 are reversed, i . e .

[0093] Vehicle speed >= 0

[0094] Tyre press change rate < ThrIMPL_prschng

[0095] On the basis of the logic state of block BRW, the switch module SW3 determines the bias to be applied to the values of the inflation pressure . I f the logic state is the state BRI , the module SW3 assigns to the bias the latest known / calculated value , because it is impos sible to calculate further values ( SW3 switches to OFF) . I f the logic state is BR2 , the module SW3 assigns to the bias the calculated value , outputting the data TP_BF, TP_BR . I f the logic state is BR3 , the switch module SW3 is bypassed, and the bias is ignored for the reasons provided in the foregoing . The logic state BR3 also leads to the generation of the implaus ibility signal o f bias BNR .

[0096] Referring to Figure 4 , the functional integration between the method according to the invention and the vehicle is implemented both by means of software , through the communication with control units on board the vehicle ( through CAN network, for example ) , and by means of hardware , by imparting the commands necessary to achieve the calculated locking torque to the various actuators adapted to operate such an intervention . More specifically, reference 100 denotes a main driveline controller, wherein the method according to the invention is implemented . In Figure 4 , the solid lines ending with a black dot represent a so ftware interface on a CAN or CAN FD network, or generally speaking on a communication bus , while the solid lines ending with an arrow represent a hardware interface , wherein the direction of the arrow indicates the direction of imparting the command .

[0097] The controller 100 exchanges data with a tyre pressure controller 102 , an airbag controller 104 , a friction brake controller 106 , an active suspension controller 108 ( i f present ) and an actuating device for active elements of the driveline on each axle 110 . Speci fically :

[0098] - the software interface with the controller 102 outputs the data TP_FR, TP_FL, TP_RR, TP_RL,

[0099] - the software interface with the controller 104 outputs the vehicle accelerations along the axes x, y, z ( longitudinal , transverse , vertical ) ,

[0100] - the software interface with the controller 106 outputs the data of the braking torques applied onto each of the four wheels of the vehicle and about the speeds of the individual wheels of the vehicle , and sends to the controller 106 the data of the target locking torques on the four wheels ( i . e . , where the actuators perform their respective action) ,

[0101] - the software interface with the controller 108 outputs the raw data of each suspension ( travel and, i f available , chamber pressure of each active suspension) ,

[0102] - the software interface with device 110 outputs the status information of the corresponding devices for applying the locking torques , and sends to device 110 the values of the target locking torques which have been determined by means of the method according to the invention ( 32 F, 32R) .

[0103] As regards the hardware interfaces , the controller 108 communicates with a set of suspension sensors 202 ( input ) and with suspension actuators 204 ( output ) , in the same way as the controller 106 communicates ( output ) with the actuators of the friction brakes .

[0104] The controller 100 communicates directly with sensors and locking actuators 206 , 208 of the axles , in the same way as the device 110 communicates with the corresponding devices for applying locking torques ( e . g . an electronically controlled limited slip di f ferential 210 ) . Generally speaking, in the outfitting of a normal vehicle there is provided either an action of the actuators and of the sensors 206, or an action of the devices 210 , because generally an outfitting having both alternatives is not provided .

[0105] The person skilled in the art will appreciate how the invention provides a method of pre-emptive calculation of locking torques based on status information which is normally present on board a vehicle , which enables avoiding the presence of special sensor equipment . Moreover, the functional integration of the method according to the invention is widely applicable , as shown in Figure 4 , and the deductive logic implemented in the method according to the invention is moreover extremely reliable because it is based, inter alia, on multi-level plausibility / reliability checks .

[0106] Of course , the implementation details and the embodiments may amply vary from what has been described and illustrated in the foregoing, without departing from the scope of the present invention, as defined in the annexed claims .

Claims

CLAIMS1. A method for determining a torque transfer between wheels of the same axle of a motor vehicle, comprising- acquiring, for each wheel of the axle, at least one of a value of the internal pressure of a tyre of the wheel (TP_FR, TP_FL, TP_RR, TP_RL) and a value of travel of a suspension associated with the wheel (ST_FR, ST_RR, ST_RL) ,- determining, on the basis of said at least one of a value of an internal pressure of a tyre of the wheel (TP_FR, TP_FL, TP_RR, TP_RL) and a value of travel of a suspension associated with the wheel (ST_FR, ST_FR, ST_RR, ST_RL) , a value of load acting on each wheel of the axle,- determining a difference between the values of the loads acting on the wheels of the axle (D24R, D24F) , and- determining a value of a locking torque for the axle (32R, 32F) as a function of said difference between the values of the loads acting on the wheels of the axle.

2. The method according to claim 1, comprising acquiring, for each wheel of the axle, the value of the internal pressure of a tyre of the wheel TP_FR, TP_FL, TP_RR, TP_RL) and the value of the excursion of a suspension associated with the wheel (ST_FR, ST_FR, ST_RR, ST_RL) .

3. The method according to claim 1 or claim 2, wherein said load value acting on each wheel of the axle is a vertical load value.

4. The method of any one of the preceding claims, comprising determining a value of a locking torque for the axle (32R, 32F) as a function of said difference between said values of the loads acting on the wheels of the axle and a target torque for the axle (20F, 20R) .

5. The method according to claim 4, wherein said determining the value of the locking torque for the axle (32R, 32F) comprises determining a zero value of said locking torque when a torque value transmissible by the axle wheel subjected to the lower load exceeds 50% of the target torque value for the axle.

6. The method according to any one of the preceding claims, comprising defining an enabling condition for applying a locking torque for each axle (18F, 18R) , wherein said determining a value of the locking torque for the axle (32R, 32F) as a function of said difference between the values of the loads acting on the wheels of the axle comprises assigning a predetermined value to the locking torque if the enabling condition is not met.

7. The method according to claim 6, wherein said predetermined value is 0 Nm.

8. The method according to any one of the preceding claims, wherein the value of the load acting on each wheel of the axle is determined on the basis of said at least one of the value of the internal pressure of a tyre of the wheel (TP_FR, TP_FL, TP_RR, TP_RL) and a value of travel of a suspension associated with the wheel (ST_FR, ST_RR, ST_RL) by means of one-dimensional maps (LUT_L, LUT_R, LUT_DP) .

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