A METHOD AND SYSTEM FOR MONITORING THE TYRE FOOTPRINTS OF A MOTOR VEHICLE, PARTICULARLY FOR AUTOMATICALLY OPTIMISING THE BEHAVIOUR OF THE MOTOR VEHICLE

Abstract: The monitoring of the footprints (Z) of the tyres (P), preferably by means of piezoresistive rubber sensors (1) incorporated in the tyres (P), enables the bearing forces to be distributed automatically amongst the various tyres (P) so as to optimise the behaviour of the motor vehicle, for example, in dependence on different driving styles or in dependence on different ambient conditions.

Description: DESCRIPTION A method and system for monitoring the tyre footprints of a motor vehicle- particularly for automati ally op imising the behaviour of the motor vehicle Background of the invention In recent years, with the increasing introduction of electronics to the automotive field, solutions which provide for the automatic control of one or more functions of the motor vehicle, such as, for example, the ignition, the fuel injection, the braking (in an antiskid function), the automatic engagement and disengagement of four-wheel drive, etc., have become idespread. However, the problem of the interaction between the vehicle and the ground over which it is moving has not hitherto been dealt with in a completely satisfactory manner, particularly as regards the development of the forces and moments whi h act on the individual regions bearing on the ground, that is, on the tyres. It appears to be essential to be able to tackle and resolve this problem in order to be able to produce vehicles in which the modulated management of its bearing on the ground is possible during driving. Objects and summary of the invention In order to satisfy the requirement stated above, a first aspect of the present invention relates to the fact that a motor vehicle may be considered as a system which interacts with the ground by means of the footprints of the tyres, on which continually varying families of forces and moments are established. More specifically, the object of the present invention is to provide means which enable the distribution of the forces between the various bearing regions to be controlled automati ally so as to optimise the behaviour of the motor vehicle according to the wishes of the driver and to prearranged reference programmes, for example, for normal, sports, or off-road driving or for dry, wet or snowy road conditions, etc. The invention has been developed with particular attention to its possible use in motor vehicles having four wheels all of which are driven and steerable (obviously with a braking capability) and s.re connected to the body of the motor vehicle by means of electronically-controlled suspension units. The main characte istic of the invention is the fact that the behaviour of the footprint of each tyre on the ground can be monitored. For this purpose, a further aspect of the present invention provides for the insertion of sensors, such as piezoresistive elastomer elements constituted, for example, by toroidal bands inserted in the structure of the tyre, in the tread region of each tyre. The state of the forces and moments acting on the footprint of the tyre can be monitored by means of these sensors. On the basis of the footprint—behaviour monitoring signals generated by these sensors and of other signals indicative, for example, of: — the dynamics of the centre of gravity of the vehicle, - the rotation of the wheels in the vertical plane (that is, the driving and braking forces acting about the axis of each wheel), — the rotation of the wheels in the horizontal plane (that is, the steering angle), and - the vertical movements of the wheels (that is, the forces acting on the suspension units), an automatic processing system enables the travelling conditions of the motor vehicle to be monitored in real time with separate reference to the conditions of each footprint, that is, of each wheel on the ground. As well as performing the monitoring function, the processing system of the vehicle (which usually includes a processor for each wheel, provided principally for the purposes of detecting and calculating the characte istics of the respective footprint, and an intelligent central processor which correlates the various interactions of the processors associated with the individual wheels) also has a data base in which comparison and/or reference paramete s a r e sto ed. The parameters can be modified selectively according to the specific requirements of the driver: for example, for sports driving, for more relaxed driving, or for driving with maximum attention to safety conditions. On the basis of the correlation of the va ious interactions of the processors and of the comparison of the monitoring data with the control parameters stored in its data base, the central processing system (which, at its upper level, preferably includes a so-called "expert system" with artificial intelligence functions, such as an ability to process heuristic decision-making methods) controls the various transmission, braking, steering and suspension members of the vehicle so as to optimise the performance and/or safety capabilities of the vehicle according to the driver's decisions. In particular, the system can continuously check the conditions of the footprint of each tyre and make fine adjustments (trimming) moment by moment in order to achieve the best general balance of the motor vehicle. The invention is preferably for use in a vehicle which has a mechanical-electri al-hydraulic system for the driving-braking, steering and suspension functions. Such a system includes an internal combustion engine which drives a high— ressure hydraulic pump, a set of hydraulic distributors for distributing the pressure to the various operating regions of the vehicle, hydraulic brakes-motors for each wheel, electro-hydraulic actuators for the steering, and electro—hydraulic shock-absorbei—actuators for the suspension units. A vehicle provided with a system of the type specified above has an intrinsic natural "antiskid" function, as well as an automatic differential effect both transversely (as regards the wheels associated with the same axle) and longitudinally (as regards the distribution of the forces between the various axles. The characteristics of the methods and systens which form subjects of the invention are recited more specifically in the claims which follow. Detailed description of the drawings The invention will now be described, purely by way of non-limiting example, with reference to the appiended drawings, in which: Figure 1 is a vertical median sectional view of a motor-vehicle wheel produced according to the invention, shown with some of the operating members associated therewith, Figure 2 is a three-dimensional cartesian graph showing a possible distribution of the forces and moments acting on a motor-vehicle wheel produced according to the invention, and Figure 3 shows schema i ally, in the form of a block diagram, the general architecture of a system according to the invention. Detailed descri tion of the invention In Figure 1, one of the wheels of a motor vehicle such as a motor car, not shown as a whole, is generally indi catεd 1. ccording to a solution i h is repeated in a practically identical manner in all the other wheels of the vehicle (for which detailed desc i tions will not therefore be given since they would be redundant) the y e P o he heel R a ies wi hi it, incorpo ated in its tread region, a plurality of piezoele tri sensors 1, preferably constituted by continuous or dis ontinuous to oidal bands made of piezo esistive rubber or another elastomer having the same properties and coe tensive with the tre d itself. Rubbers of this type have recently been made available commercially. The essential characteristi of these rubbers is constituted by their capacity to generate electrical signals indicative of the amount by which they are deformed, and hence of the intensity of the forces causing the deformation, in dependence on the mechanical stresses to which they a r e subject. The fact that rubbers with piezoelectric or piezoresistive characteristi s can be used instead of other types of sensors (for example, conventional extensometers or strain gauges) offers the advantage that the sensors can be incorporated in the body of the tyre P. In particular, the sensors 1 can be arranged in the tread region at a certain distance from the wearing layer of the tread so that they are at any rate protected from the outside environment. As can be seen better in the schematic view of Figure 2, in correspondence with the footprint (that is, the region 2 of the tyre P which bears on the ground), the sensors 1 (the number of which is such as to cover the monitored region with a sufficient density) follow the deformation of the tread and a r e deformed along a line which is generally chordal relative to the shape of the heel. Since the amount and state of their deformation depend on the amount and state of the deformation of the tread which in turn are determined by the intensity of the forces and moments acting on the tread and hence on the wheel as a whole, the signals generated by the sensors obviously car ry all the information relating to these forces and moments. By processing the signals provided by the sensors 1 (processing which may be carried out according to wholly known criteria that do not therefore require a specific description) the forces can be resolved according to an x, y, z cartesian system centred about the point 0 which constitutes the centre of the footprint Z, as shown schematically in Figure 2. A similar result can also be obtained relating to the moments M acting on the wheel R. In particular, the value of the local coefficent of friction | i at a ' particular time can be calculated for each wheel R of the vehicle from the footprint-monitoring signals generated by the sensors 1. With reference again to the diagram of Figure 3, a drive-shaft, indicated A, rotates the rotating bearing S to which the wheel R is fixed according to the usual criteria. The drive-shaft A is driven by a motor M constituted, in the currently preferred embodiment, by a hydraulic motor which receives the pressurised fluid necessary for its operation from an engine-pump unit MP. The unit in question is usually consti uted by the internal combustion engine of the motor vehicle and an associated hydraulic pump. The same engine-pump unit MP pilots a hydraulic actuator, such as a jack J, the rod J of whi h controls the steering movement of the wheel R A further jack K acts as a suspension unit which regulates the vertical position of the wheel relative to the body of the motor vehicle., The pipes through which the engine-pump unit MP sends the operating fluid to the hydraulic motor M and the jacks J, K are schematically indicated A, T_, T„. The passage of the operating fluid through the pipes is controlled by respective valves V,, V„ and V„ which are controlled by a distributor D governed by a central control unit according to criteria which will be ε described further below. However, it should be stated that, although the present description refers to the use of electro—hydraulic di tributors, motors and actuators for controlling the driving-braking, steering and suspension functions of the wheels, this selection should not be considered critical for carrying out the invention. In fact, the invention can also be used in connection with motors and actuators of different kinds, for example, fully electrical motors and actuators. The use of electro-mechani al or mechanical systems should also be regarded as included in the scope of the present inven ion. The progressive reference numerals 2 to 5 indicate a plurality of sensors constituted, more precisely, by: — a sensor (2) for sensing the dynamics of the centre of gravity of the motor vehicle and constituted, for example, by a sensor located substantially at the centre of gravity of the motor-vehi le body for measuring acceleration along three axes, — a sensor (3) for sensing the rate of rotation of the wheel, for example, a phonic wheel, — a sensor (5) for sensing the "vertical" position of the wheel, that is, the attitude of the suspension. Sensors which satisfy the applicational requirements described are widely known in the art and have been proposed many times for use in the automotive field. A processor, generally indicated 6 (constituted, for example, by a microprocessor or by a functional area of such a component) is connected to the sensors 1 (by the criteria used in the art for the connection, for example, of tyre-pressure sensors) as well as to the other sensors 3 to 5 just described. The function of the processor ώ is essentially to process the set of signals supplied by the various sensors so as to provide a complete picture in real time of the conditions under which the wheel is operating at any particular time, that is, the set of data relating to the forces and moments acting on the wheel and the data relating to the rate of rotation, the orientation and the "height" of the wheel relative to the vehicle body, possibly with the addition of data relating to the general kinematics of the motor vehicle, detected at the centre of gravity by the se o 2. The data generated by the processor 6 or data resul ing fro further processin o these sta ting data (for example, the data, relating to the local coe icient of friction - > aι ' e compared with cor esponding control and reference parameters stored in a data base 7. In this connection, it should be noted that a respective processor is associated with each wheel R of the vehicle. The data generated by the various processors 6 (as well as the signal generated by the accelero etri sensor 2) are then sent to a centralised, higher-level processor 8 which acts on a central control unit 8a for controlling the distributor D, possibly with adaptive feedback to the various processors 6 (line 8b). As regards the data base 7, it is therefore possible to opt for either a decentralised solution (each processor 6 having a respective data base 7 of control or reference data) or a centralised solution (the signals generated by the various processors 6 being sent to a single centralised data base 7 for comparison), or even for a hybrid solution in which some functions are decerttralised and other functions are centralised. Naturally, the selection of one solution or another is dictated by the specific requirements applying at the time in question. The purpose of the comparison with the data contained in the data base 7 is to check whether the operating conditions of each wheel at a particular time fall within a range which coincides with or deviates to an acceptable degree from the ideal conditions represented by the reference or comparison parameters stored in the data base 7. For example, a value of the coefficient of f iction^ which is considered ideal for the conditions of the road surface may be stored in the data base 7 and the value L[ detected locally at a particular time compared therewith. The driving control operations carried out by the driver are taken into account when the comparison is mad . For this purpose, respective sensors of known type are associated with the control members operated by the driver (for example, the steering wheel W, the brake pedal B and the accelerator pedal G) but only one of the sensors, that is, the one associated' with the steering box W and indicated by the reference number 9, is shown. The sensors in question send signals • 1 '1 indicative of the control operations carried out by the driver (steering, acceleration, braking, etc.) to the central processor 8 on respective output lines W,, B, nd G.... In general terms, the function of the central processor S is to transfer to the operating members of the wheel (that is, the drive motor M, the steering jack J, the suspension-control jack K) respective movement- or steering-control signals which translate the commands given by the driver when he operates the steering wheel W and the pedals B, G. However, the transmission (or rather translation) takes into account the result. of the comparison between the data relating to the operating conditions of the wheels R (generated by the processors 6 ) and the control or reference data stored in the data base or data bases 7, with the interactive correlation of the data received from the various process calculators 6. In practice, for example, if the driver operates the accelerator pedal G and attempts to impose on the vehicle an acceleration and/or a speed which is incompatible with the road-holding conditions of the wheels (as indicated by the reference or comparison data stored in the data base 7), the processor 8 modifies the acceleration signal which is effectively transmitted to the drive motors M of the wheels so as to keep the acceleration and/or speed imparted to the vehicle within the safety limits. As has been seen, the data base 7 may contain several sets of control or reference data which can be used as alternatives to one another (for example, in the form of memory arrays which can be introduced alternatively by the user a will). The comparison data or parameters, that is, the level of criticality of the travelling conditions to be reached can thus be varied selectively: for example, it is thus possible to choose a closer approach to critical conditions if a sporting style of driving is desired or - for example, when the vehicle is entrusted to a learner driver - to choose to restrict the performance of the motor vehicle to the conditions of maximum safety. To advantage, the processor 8 may be arranged so that it is brought automatically to the latter condition when a breakdown is detected. The management achieved by the system in a motor vehicle with four driven and steerable wheels is extremely flexible to the extent that it even enables apparently conflicting commands to be imparted to the various wheels, for example, to increase the rate of rotation of some wheels whilst braking others, to modify the steering attitude of one wheel even to an attitude opposite that which would be imparted thereto in a conventional steering system, or even selectively to modify the suspension characteristics of the various wheels even in competition with each other. This independent control function for each wheel can easily be achieved by the processor 8 through the central control unit 8a (which can also be produced either in a decentralised form - with a module for each wheel — or in a centralised form - with a single centralised control unit) by means of the distributor or distributors D which control the valves V.,, V„ and V_ for controlling the supply of operating fluid to the motors M and the jacks J and K. It is thus possible for the motor vehicle as a whole to be configured as a system which interacts with the road by means of the footprints Z of the tyres, by virtue of the monitoring of the continually varying forces and moments acting thereon. It is thus possible automati ally to control the distribution of these forces between the various tyres, that is, between the various bearing regions of the vehicle, so as to optimise the behaviour of the motor vehicle according to the wishes of the driver and to prearranged reference programs, perhaps even for different driving styles or for different road-surface conditions.

Claims: CLAIMS 1. A method for controlling the movement of a motor vehicle provided with tyres (P) which cooperate with the ground to define respective footprints (Z) , characte ised in that it includes the steps of: - monitoring CD the behaviour of the footprints and generating at least one respective footprint signal indicative of the behaviour of the footprints (Z), and - using (6 to Sa) the at least one footprint signal to control the movement of the motor vehicle. 2. A method according to Claim Λ , characterised in that the at least one footprint signal is generated by monitoring (D the deformation of the tyre (P), the deformation being indicative of the forces and moments acting on the tyre (P). 3. A method according to Claim 1 or Claim 2, characterised in that it includes the step of proces¬ sing the at least one footprint signal, the processing (6) including a step in which the signal is compared with at least one reference or control datum previously stored in a memory (7). 4. A method according to Claim 3, characterised in that the at least one stored reference or control datum (7) can be varied selectively according to different driving conditions or different ground conditions. 5. A method according to any one of Claims 1 to 4, characterised in that it includes the step of detecting (W, r B. G.) at least one driving control signal generated by the driver of the motor vehicle and then processing the at least one driving control signal in dependence on the at least one footprint signal (Z), with a view to controlling the movement of the motor vehicle. 6. A method according to any one of the preceding claims, characterised in that at least one respective footprint signal ( Z ) is generated for each wheel (R) of the motor vehicle, and in that the footprint signals generated for the various wheels (R) of the motor vehicle a re used in a correlated manner for controlling the movement of the motor vehicle. 7. A method a ording to any one of the pre eding claims, characte ised in that it includes the step of selectively controlling, in dependence on the at least- one respective footprint signal (Z), at least one of the physical quantities selected from the group constituted by: - the rate of rotation of the wheels (M) , - the steering angle of the wheels (J), and - the attitude of the suspension units of the wheels (K). S. A method according to Claim 7, characterized in that the quantities included in the said group are controlled primarily by electrical, electro-mechani al or mechanical means (M, J, K). 9. A method according to Claim 7, characterised in that the quantities included in the said group are controlled primarily by fluid-operated means ( M, J, K ) . •10. A method according to any one of the preceding claims, characterised in that it includes the step of generating at least one sensor signal selected from the group constituted by: - a signal (2) indicative of the dynamics of the centre of gravity of the motor vehicle, - a wheel—rotation signal (3), - a signal (4) indicative of the steering angle of the wheels, and - a signal (5) indicative of the attitude of the suspension units of the wheels, and in that the at least one sensor signal is processed (6) with the at least one footprint signal (Z) for use in controlling the movement of the motor vehicle. 11. A method according to any one of the preceding claims, characterised in that it includes the step of controlling in a coordinated manner, using the at least one respective footprint signal (Z) and for all the wheels (R) of the motor vehicle, the following physical quan ities: — the rate of rotation of the wheel, — the steering angle of the wheel, and — the attitude of the suspension of the wheel. 12. A method according to Claim 11, characterised in that respective footprint signals are generated for all the wheels (R) of the motor vehicle. 13. A method according to Claim 3 or Claim 4, characterised in that the movement of the motor vehicle is controlled automatically with the use of: - a first-level processing capability (6, 7) associated with each wheel (R> of the motor vehicle for detecting the at least one footprint signal and comparing it with the at least one reference or control datum for each wheel (R) of the motor vehicle, and — a second-level processing capability (8) which can control the movement of the motor vehicle (8a, D) in dependence on messages received from the first-level processing capabilities associated with the various wheels (R) of the motor vehicle. 14. A method according to Claim 13, characterised in that it includes the step of applying artificial intelligence methods in the second-level processing capabi1i y. 15. A system for controlling the movement of a motor vehicle provided with tyres (P) which cooperate with the ground to define respective footprints (Z), characterised in that it includes: - monitoring means (1) which are sensitive to the behaviour of the footprints (Z) and can generate at least one respective footprint signal indicative of the behaviour of the footprint (Z), and - processing means (6 to 8) and control means (C, D) which can use the at least one footprint signal to control the movement of the motor vehicle. 16. A system according to Claim 15, characte ised in that the monitoring means ar e sensitive to the deformation of the tyre (P), the deformation being indicative of the forces and moments acting on the tyre (P) . 17. A system according to Claim 15 or Claim 16, characterised in that it includes comparison means (6, 7) for comparing the at least one footprint signal with at least one reference or control datum previously stored in a memory (7). 18. A system according to Claim 17, characte ised in that the comparison means (6, 7) include separate memory functions so as to vary selectively the at least one reference or control datum according to different driving conditions or different ground conditions. 19. A system according to any one of Claims 15 to 18, characterised in that it includes means (W , B. , G ) for detecting at least one driving control signal generated by the driver of the motor vehicle and then processing the at least one driving control signal in dependence on the at least one footprint signal, with a view to controlling the movement of the motor vehicle. 20. A system according to any one of the preceding Claims 15 to 19, characterised in that it has sensor means (1) for generating at least one respective footprint signal for each wheel (R) of the motor vehicle, and processing means (2) for correlating the footprint signals generated for the various wheels ( R ) of the motor vehicle for use in controlling the movement of the motor vehicle. 21. A system according to any one of the preceding Claims 15 to 20, characterised in that actuator means are provided for controlling selectively, in dependence on the at least one respective footprint signal, at least one of the physical quantities selected from the group constituted by: - the rate of rotation of the wheels, - the steering angle of the wheels, and - the attitude of the suspension units of the wheels. 22. A system according to Claim 21, characterised in that the actuator means are constituted primarily by fluid actuator means (M, J, K ) . 23. A system according to any one of the preceding Claims 15 to 22, characterised in that it also includes sensor means selected from the group constituted by: - a sensor (2) for sensing the dynamics of the centre of gravity of the motor vehicle, - a sensor (3) for sensing the rate of rotation of the wheels, - a sensor (4) for sensing the steering angle of the wheels, and - a sensor (5) for sensing the attitude of the suspension units of the wheels (5), and in that the signals generated by the sensors (2 to 5) are processed (6) with the at least one footprint signal for use in controlling the movement of the motor vehi l . 24. A system according to any one of Claims 15 to 23, characte ised in that all the wheels of the motor vehicle a r e provided with actuator means (M, J, K) for controlling: - the rate of rotation of the wheel, - the steering angle of the wheel, and - the attitude of the suspension of the wheel. 25. A system according to Claim 15, characterised in that, for controlling the movement of the motor vehicle, there are provided: - first-level processing means (6, 7) which are associated with each wheel (12) of the motor vehicle and can detect the at least one tread signal and compare it with the at least one reference or control datum for each wheel of the motor vehicle, and - second-level processing means (8) which can control the movement of the motor vehicle (3a, D) in dependence on messages received from the first-level processing means (8) associated with the various wheels (R) of the motor vehicle. 26. A system according to Claim 25, characterised in that the second-level processing means (8) include an expert system. 27. A method of monitoring the footprint (Z) of a motor vehicle tyre (P> on the ground, characterised in that it includes the step of incorporating in the flexible structure of the tyre (P) extensometric transducer means (1) which can deform as a result of the tyre bearing on the ground, and thus generate signals indicative of the behaviour of the footprint (Z) . 28. A method according to Claim 27, characterised in tha.t piezoelectric or piezoresistive elastomers are used to form the extensometri transducer means. 29. A method according to Claim 27 or Claim 28, characterised in that the extensometric transducer means (1) are arranged in toroidal formations substantially coextensive with the tread of the tyre. 30. A method according to any one Claims 27 to 29, characterised in that it includes the step of inco porating the extensometric transducer means CD in the tread of the tyre CP). 31. A method according to Claim 29 or Claim 30, characterised in that it includes the step of incorporating the extensometric transducer means (1) in the flexible structure of the tyre at a certain distance from the wearing surface of the tread. 32. A device of monitoring the footprint (Z) a motor vehicle tyre on the ground, characterised in that it includes extensometric transducer means (1) incorporated in the flexible structure of the tyre and able to deform as a result of the tyre bearing (P) on the ground, so as to generate signals indicative of the behaviour of the bearing region (Z) of the tread. 33. A device according to Claim 32, characterised in that the extensometri transducer means comprise transducers made from piezoelectric or piezoresistive elasto er . 34. A device according to Claim 32 or Claim 33, characte ised in that the extensometri transducer means are formed as toroidal formations ( 1 ) substantially coextensive with the tread of the tyre. 35. A device according to Claim 34, characte ised in that the extensometri transducer means ( 1 ) are incorporated in the tread of the tyre. 36. A device according to Claim 34 or Claim 35, characterised in that the extensometri transducer- means (1) are located at a certain distance from the wearing surface of the tread.

Inventors: FIORAVANTI LEONARDO, FIORAVANTI, LEONARDO
Applicants: FIORAVANTI LEONARDO, FIORAVANTI, LEONARDO
Application year: 1989
Main classification: B60G17
IPC codes: B60C23, B60G17, B60W10, B62D6, B62D113, B62D137