Method and system for estimating the lean angle of a moving vehicle

Abstract

The present invention relates to the field of control systems of cornering vehicles. In particular, the invention relates to a system for detecting operating state conditions of a moving vehicle. Such conditions include : lateral slope of the road, lean angle ( the lean angle is the angle formed between the longitudinal axis of the vehicle and the travel direction), forces exchanged between the tire and the road in the lateral direction, and stiffness of a tire. The present invention also relates to a method for detecting the states of the cornering vehicle by measuring the displacement of the brake disc, due to the kinematics related to hub backlash and due to the hub deformation itself related to wheel loads.

Description

[0001] Method and system for estimating the lean angle of a moving vehicle

[0002] To: Brembo S.p.A.

[0003] Inventors: Leonardo De Novellis, Fabio Carbone, Fabrizio

[0004] Forni

[0005] Field of the invention

[0006] The present invention relates to the field of control systems of cornering vehicles. In particular, the invention relates to a method and system for detecting the operating state conditions of a moving vehicle. Such conditions include lateral slope of the road, lean angle (the lean angle is the angle formed between the longitudinal axis of the vehicle and the travel direction) , forces exchanged between the tire and the road in the direction transverse to the travel direction, and stiffness of a tire.

[0007] Vehicles can include, inter alia, motorcycles, cars, buses or commercial vehicles, lorries.

[0008] The present invention also relates to a method for detecting the states of the cornering vehicle by measuring the displacement of the brake disc, due to the kinematics related to hub backlash and due to the hub deformation itself related to wheel loads.

[0009] Background art

[0010] For controlling the stability of a cornering vehicle, it is of great value to estimate the forces exchanged between tire and asphalt, the lean angle, i.e., the vehicle dri ft state with respect to the traj ectory ( yaw, roll ) , and the lateral slope of the road as accurately as possible . Such information is di fficult to estimate because it is related to variations in tire condition and type , operating conditions , and asphalt conditions . An incorrect or inaccurate detection of such information leads to an incorrect or inaccurate estimation of the vehicle steering conditions , and thus to incorrect or failed activations of the stability control systems of the vehicle itsel f .

[0011] In order to detect such information, in the vehicle stability systems it is known to employ algorithms based on theoretical models , which use data measured by sensors mounted on the vehicle , such as gyroscope , accelerometer, steering angle sensor, wheel revolution sensors , GPS , for example . In these cases , the measurement system is based on numerical methods which utili ze the equilibrium equations of the vehicle or parts thereof , or on estimation methods based on "observers" according to the control theory .

[0012] However, such estimation modes exhibit limitations and inaccuracies .

[0013] The main limitation is that such systems are based on parameters which must be known in advance , the knowledge of which is not immediate and the change of which during the vehicle li fe impacts the estimation accuracy . Another limitation is due to the computational cost of such algorithms to be implemented at " runtime" on the control units mounted aboard the vehicle . Therefore, the need arises to have a detection system which, by employing compact and miniaturized sensor, which are simple to activate / read, allows determining the cornering states of the vehicle with high accuracy and reliability.

[0014] As already noted above, such needs are not fully met by the solutions currently available from the prior art.

[0015] There are several patents and publications in the scientific literature which allow estimating the tire cornering forces, the yaw angle, and the roll angle. Most of them use information from traditional sensors already available on the control units of the vehicle (i.e., yaw speed sensor, accelerometers, steering wheel angle sensors) to estimate the aforementioned vehicle states with a variety of algorithms and techniques.

[0016] The main disadvantage of accelerometers used to measure the vehicle state is that, in the presence of a lateral inclination angle of the road, the output signal is affected by an error due to the gravity acceleration. In order to avoid erroneous interventions of the cornering stability control systems (e.g., ESP, VDC, DYC, to name just a few) because of the lateral inclination angle, a non-intervention threshold is often included in the algorithms for controlling such systems, but at the expense of a less responsive stability control system.

[0017] Other solutions require the use of GPS sensors (such as that in W02012001825A1 ) , with an obvious lack of accuracy . US2010100272A1 describes displacement sensors connected to suspension elements to estimate the road inclination angle , however the use of GPS is necessary with related lack of accuracy and delays .

[0018] EP3023761A2 allows estimating the vehicle cornering forces using accelerometers positioned on angular elements and software .

[0019] EP3153374A1 suggests estimating tire forces from the signals available on CAN bus and coming from sensors , the data concern acceleration and one or more angular speeds , steering wheel angle , angular wheel speed, roll speed, pitch speed, and yaw speed; thi s is the current state of development for production vehicles .

[0020] Patents such as US2008294355A1 , CN104527775A introduce the estimation of lateral forces of the tire using electric power steering, but the estimation accuracy is not suf ficient for many needs .

[0021] Another possibility is to use sensori zed bearings ( SKF) : IT102021000030599 and IT102020000020608 allow estimating the tire forces using a speci fic sensori zed bearing on wheel hub : thi s obviously has an impact on the vehicle / j oint assembly, cost , and flexibility .

[0022] Again, EP1021326 describes a method for determining the vehicle state variables based on the forces applied to the individual wheels . The forces are detected with the aid of sensors installed in the tires , where the measured variables represent the longitudinal , lateral and vertical forces of the tire . The yaw angle of the vehicle , the angular yaw acceleration thereof , the steering angle , dri ft angle , speed and acceleration are determined by including correction variables detected, estimated and calculated in corresponding correction steps .

[0023] The need is felt for a method of estimating vehicle travel states which is easy to implement , inexpensive , and accurate in the estimates .

[0024] Purpose and object of the invention

[0025] It is an obj ect of the present invention to provide a system for detecting operating state conditions associated with the movement of a cornering vehicle . In particular, the invention relates to a system for detecting the states of a vehicle , which allows overcoming, at least partially, the limitations and drawbacks of the solutions available in the prior art .

[0026] It is a further obj ect of the invention to provide a system which also allows obtaining and providing an indirect measurement of the lateral slope of the road .

[0027] It is a further obj ect of the invention to provide a system which further allows obtaining and providing an indirect measurement of the vehicle lean angle .

[0028] It is a further obj ect of the invention to provide a system which allows obtaining and providing an indirect measurement of the forces exchanged between tires and road in the transverse direction .

[0029] The present invention relates to a method and a system according to the appended claims .

[0030] Detailed description of embodiments of the invention List of drawings

[0031] The invention will now be described by way of a nonlimiting illustration, with particular reference to the figures in the accompanying drawings, in which:

[0032] - figure 1 shows, from (a) to (c) , a diagrammatic and enlarged view of an embodiment of the system for detecting operating state conditions associated with the movement of a vehicle, in which two sensors are positioned on either side of a vehicle axle in order to measure the lateral road-tire forces insisting on the axle;

[0033] - figure 2 shows, in a simplified manner, the dynamic diagram of a motor vehicle under acceleration when cornering to the left: indeed, there are shown the longitudinal inertia force (FX,IN) , the inertia force acting in the transverse direction (FX,IN) , the forces exchanged between tires and road at the four wheels in the longitudinal direction (FX,FL front left wheel, FX,FR front right wheel, FX,RL rear left wheel, FX,RR rear right wheel) and in the transverse direction (FY,FL front left wheel, FY,FR right front wheel, FY,RL left rear wheel, FY,RR right rear wheel) , according to the prior art;

[0034] - figure 3 diagrammatically shows an embodiment of a system for detecting operating state conditions associated with the movement of a vehicle, in which two sensors are positioned on either side of a vehicle axle in order to measure the lateral roadtire forces insisting on the axle during a general configuration of a vehicle when cornering to the left;

[0035] - figure 4 shows possible alternative embodiments of a measurement diagram, in which two sensors are applied to the same disc at both ends of the diameter (1.) , to the inner and outer sides of the same disc (2.) , or to two discs on the same axle (3.) ; in all three cases, the measurement is read by a control unit (ECU) in which the algorithms 1., 2., 3. are present;

[0036] - figure 5 shows a track test during a lateral dynamics (skid pad) test, in which the signal from the sensor, mounted at the right front wheel, is plotted with respect to the lateral acceleration: such a test is confirmation that the response of the sensor is linked to the lateral acceleration of a cornering vehicle, and can thus be used for the vehicle state estimation algorithms;

[0037] - figure 6 shows the trend of the transverse force (Fy) of the right front wheel as the lateral acceleration changes during a simulated skid pad test ;

[0038] - figure 7 shows, by means of a flow chart, the first algorithm useful for lateral dynamics: once the sensor has been calibrated with respect to the lateral tire-road forces (Fy) , with tests or simulations, it is possible to use the other sensors installed on the vehicle and the equation of balance of the lateral forces to calculate the lean angle P ; and - figure 8 shows , by means of a flow chart , the operating steps of the method for indirectly measuring the lateral slope cp of the road .

[0039] It is here speci fied that elements of di fferent embodiments can be combined to provide additional embodiments , without restrictions , by respecting the technical concept of the invention, as those skilled in the art will ef fortlessly understand from the description .

[0040] The present description also refers to the prior art for the implementation thereof in relation to the detail features not described, such as elements of minor importance usually used in the prior art in solutions of the same type , for example .

[0041] When an element is introduced, it is always understood that there can be " at least one" or "one or more" .

[0042] When a list of elements or features is given in this description, it is understood that the finding according to the invention " comprises" or alternatively " consists of" said elements .

[0043] When listing features in the same sentence or bul let list , one or more of the single features can be included in the invention without connection with the other features in the list .

[0044] Embodiments

[0045] The obj ects of the invention are achieved by a system for detecting the displacement o f a brake disc of a cornering vehicle . With reference to Fig. 1, in an embodiment of the invention, an eddy current sensor (disc monitoring sensor) 20 coupled to a brake disc 150 and placed at a given distance from the disc, in the general front view (a) of a brake caliper 100, is used. The sensor 20 is positioned inside a brake caliper 100 or on any other element of the wheel hub (e.g., hub carrier or additional bracket, motorcycle swingarms / support feet for motorcycle swingarm calipers) . It is also possible to position a temperature sensor 30 inside the brake caliper 100. It is also possible to position an additional temperature sensor (not shown) inside the pad 60, preferably in the plate. The wheel hub 160 of the vehicle on which the disc and the eddy current sensor of the invention are mounted is also shown in the figure. Fig. 1 (b) shows a front view of the brake caliper 100.

[0046] In greater detail, the eddy current sensor is inserted into a brake caliper and placed at 2-10mm, preferably at 4-6mm from the brake disc. The distance to be used is also a function of the different dimensions of the sensor actually used. It is also possible to install the sensor on any other element of the wheel hub or hub carrier, therefore even not necessarily inside a brake caliper. Fig. 4 shows various mounting modes, in which two sensors 20 are applied to the same disc 200 at both ends of the diameter (1.) , to the inner and outer sides of the same disc (2.) or to two discs on the same axle (3.) ; in all three cases, the measurement is read by a control unit (ECU) in which algorithms corresponding to cases 1., 2., 3. are present. The eddy current sensor 20 in Fig. 1 (c) consists of a ferrite core 21 wound by a conductive coil 22. It is powered by an electronic control unit (not shown) , which can be positioned close to the caliper or on the chassis of the vehicle. The use of fixed or floating calipers, as well as fixed or floating discs, made of cast iron, steel or carbon variants, can be considered as further embodiments of the invention.

[0047] The eddy current sensor is, in turn, connected to an electronic power supply and output signal conditioning unit. Such a control unit can be integrated into the sensor itself or connected to the sensor by means of a cable. The sensor, connected to the aforesaid control unit, provides two pieces of information: information concerning an inductance measurement and information concerning a resistance measurement. The inductance measurement refers to the measurement of the inductance value of the eddy current sensor when it is magnetically coupled to the brake disc: such an inductance value varies as the relative distance between sensor and brake disc varies.

[0048] The sensor thus allows detecting any relative movement of the brake disc with respect to the head of the sensor itself.

[0049] Figure 2 shows, in a simplified manner, the dynamic diagram of a motor vehicle under acceleration when cornering to the left: there are shown the longitudinal inertia force (FX,IN) , the inertia force acting in the transverse direction (FX,IN) , the forces exchanged between tires and road at the four wheels in the longitudinal direction (FX,FL front left wheel, Fx, FR front right wheel, FX,RL rear left wheel, Fx,RR rear right wheel) and in the transverse direction (Fy,FL front left wheel, FY,FR right front wheel, Fy,RLleft rear wheel, Fy,RRright rear wheel) , according to the prior art.

[0050] With reference to Fig. 3, a relative movement between the vehicle chassis and the unsprung masses occurs when cornering, caused by the suspension geometry. Furthermore, the lateral tire forces act on the wheel hubs 300, generating overturning and deformation of the wheel hub itself. The latter effect contributes to generating an angular displacement between the caliper 100 and the disc 200, i.e., between the disc 200 and the chassis 500, referred to as disc tilting . Such an angular displacement can be measured by the sensor 20 and can have different values for each tire 400.

[0051] The greater the lateral force of tire 400, the greater the angular displacement 0. This means that the angular displacement measured by the sensor can be correlated to the lateral forces Fyacting on the wheels, in particular the left (FL) and right (FR) wheels. This applies to any vehicle axle, whether it is a car with two axles or a lorry with three or more axles. As known, the generation of lateral forces Fyresulting from the tire-road contact is a consequence of the presence of an inertia force Fin in the transverse direction, determined by centripetal acceleration during a curvilinear motion.

[0052] This has been demonstrated by vehicle tests carried out by the Inventors. With reference to Fig. 4, the knowledge of the lateral forces of the tire can be utili zed in a vehicle dynamics control algorithm to estimate a variety of vehicle magnitudes : in other words , the aforesaid sensor measurement and the correlation of the lateral forces of the tire can be converted into data structures and stored in the vehicle control unit 600 , with the advantage of better estimating the yaw angle or roll angle , with greater accuracy than other control strategies .

[0053] According to an aspect of the invention, knowing the lateral tire forces , multiple algorithms can be developed to evaluate the other vehicle states ( yaw angle , roll angle ) . The advantage of such a method is that a sensor can be mounted on each wheel of the vehicle , thus di scriminating between di fferent driving conditions and providing more accurate information on the wheel behavior to the computational algorithms .

[0054] As for the measurement of lateral forces , a predetermined data structure could be prepared and included in the software algorithm as a feedforward approach ( according to the control theory) and used to determine the lateral force Fy for each angle in order to :

[0055] - estimate the lateral inclination angle of the vehicle in the presence of a lateral slope in an accurate manner ; and / or

[0056] - adj ust the reference yaw speed (ESP ) in the presence of lateral slope ; and / or

[0057] - separate the yaw and roll angle estimation for better control of roll angle ; and / or - evaluate the tire stiffness to lateral forces when different tire sets are mounted on the vehicle, allowing the automatic adaptation of vehicle stability control (such as ESP, VDC, etc., for example) .

[0058] In the typical embodiment, the eddy current sensor is placed in front of a brake disc, inside a brake caliper. The sensor is connected to a cable, connected to an electronic unit of the sensor which processes the sensor output into an analog / digital signal capable of being processed by other ECUs of the vehicle.

[0059] The electronic unit of the sensor can be embedded inside the sensor itself.

[0060] Different architectures can be provided (see Fig. 4) : two diametrically opposite sensors for each brake disc (1.) , two sensors on the two flat faces of the disc (2.) , one sensor in front of one of the two faces of the brake disc ( 3. ) .

[0061] In all cases, the information from the sensors is sent to the control unit (ECU) . It is possible to provide for the information from sensors traditionally installed on vehicles, such as accelerometers for measuring longitudinal and lateral accelerations, gyroscope for measuring yaw speed, steering angle sensor for measuring steering angle, can also reach such a control unit. Accelerometers and gyroscopes are known to be embedded in a unit referred to as an "inertial platform", with which every vehicle is equipped nowadays.

[0062] With reference to Fig. 5, in which the signal from the sensor, mounted on the right front wheel of a C- segment vehicle , is plotted against the lateral acceleration, early lateral dynamics tests ( in particular, skid pad tests ) on the track have shown a good correlation between the raw output values of the sensor and the measured lateral acceleration .

[0063] Therefore, a skid pad maneuver was simulated on a computer and the trend of the right front lateral force as a function of the lateral acceleration of the vehicle was evaluated ( figure 6 ) : it can be seen that the trend is very similar to the signal of the sensor depicted in Fig . 5 .

[0064] Figure 7 shows , by means of a flow chart , the first algorithm useful for estimating the lateral dynamics ; once the sensor has been calibrated with respect to the lateral tire-road forces ( Fy) , with tests or simulations ( compare Figs . 5 and 6 ) , it is pos sible to use the other sensors installed on the vehicle and the lateral force balance equation to calculate the lean angle It is possible to install at least one eddy current sensor at each wheel of the vehicle . For a car , 4 installed sensors are thus considered .

[0065] The first block 710 measures the yaw r from the above sensor .

[0066] The second block 720 calculates the steering angle 6wiof the i-th wheel from a steering wheel angle sensor ( the relationship between wheel steering angle and steering wheel steering angle is obtained from the steering kinematics relationship and usually provided by the vehicle manufacturer ) . The third block 730 provides the derivative V of the forward speed V of the vehicle , information measured by the accelerometer of the inertial platform .

[0067] In the fourth block 740 , the value of the lateral force Fyi, related to the i-th wheel , is then obtained from the signal measured by the eddy current sensor as a function of the calibration curve .

[0068] The fi fth block 750 calculates the lean angle of the vehicle as a function of the estimated vehicle mass , the vehicle forward speed ( obtained based on estimates ) , the derivative of the lateral speed ( obtained by means of the inertial platform accelerometer ) , the longitudinal forces estimated based on the longitudinal acceleration and the vehicle mass or knowing the drive / braking torque on the wheel , and as a function of the vehicle yaw ( from the gyro sensor ) and the wheel steering angles .

[0069] For example , the following equation is used to calculate the lean angle P, where m is the estimated mass of the vehicle . ur)

[0070] This occurs considering that " u" is the vehicle forward speed estimated by software modules according to the prior art ( e . g . , by averaging the angular speeds of the wheels ) . The longitudinal forces Fxiare estimated by means of longitudinal acceleration and vehicle mass or by knowing the drive / braking torque on the wheel . Figure 8 illustrates , by means of a flow chart , the operating steps of the method for indirectly measuring the lateral slope < / > of the road . The prerequisite is the calibration of the signal of the eddy current sensor with respect to the transverse force Fyof the wheel ( compare Figs . 5 and 6 ) .

[0071] In the first block 810 , the yaw speed r is measured by the gyro sensor .

[0072] In the second block 820 , the derivative V of the lateral speed is measured by means of the accelerometer of the inertial platform . The lean angle fl is obtained by means of estimation algorithms according to the prior art .

[0073] In the third block 830 , the steering angle SWiof the i-th wheel is calculated from a steering angle sensor and steering kinematics .

[0074] In the fourth block 840 , the lateral force of the i- th wheel Fy± is derived from the measurements of the eddy current sensors , by virtue of the calibration curve explained above .

[0075] In the fi fth block 850 , the lateral slope < / > of the road is calculated as a function of the estimated vehicle mass , the gravity acceleration, the vehicle forward speed ( obtained based on estimates ) , the derivative of the lateral speed ( obtained by means of the inertial platform accelerometer ) , the longitudinal forces estimated based on longitudinal acceleration and vehicle mass or by knowing the drive / braking torque on the wheel , and as a function of the vehicle yaw ( from the gyro sensor ) and the wheel steering angles . For example, the following equation is used: where m is the estimated vehicle mass and g is the acceleration of gravity (equal to 9.81 m / s2) . " u" is the vehicle forward speed estimated by software modules according to the prior art. The longitudinal forces Fxiare estimated from longitudinal acceleration and vehicle mass or knowing the drive / braking torque on the wheel.

[0076] In the sixth block 860, the yaw speed measured by the gyroscope (and affected by error) is corrected (optionally) . It is also possible to correct the reference yaw speed of the stability control system (e.g. , ESP) .

[0077] Two or more of the parts (elements, devices, systems) described above can be freely associated and considered as a kit of parts according to the invention.

[0078] Preferred embodiments have been described above and variations of the present invention have been suggested, but it should be understood that those skilled in the art may make modifications and changes without departing from the related scope of protection, as defined by the appended claims.

Claims

CLAIMS1. A method (700) for estimating the operating state conditions of a forward-moving vehicle comprising at least one wheel provided with a tire and a brake disc (150) , as well as an inertial platform, wherein an eddy current sensor (20) coupled to the brake disc (150) and placed at a given distance from the brake disc is used for each of the at least one wheel, the method comprising performing the following steps:A. calibrating the eddy-current sensor (20) with respect to the lateral tire-road forces (Fy) by means of tests or simulations, determining a calibration curve;B. determining (710) a yaw r from the signal acquired by a gyro sensor;C. calculating (720) a steering angle 6wiof the i-th wheel of the at least one wheel based on the signal acquired by a steering angle sensor;D. determining (730) the derivative V of the vehicle forward speed V, based on a signal acquired by an accelerometer placed on the inertial platform;E. obtaining (740) the value of the lateral force Fy±, with respect to the i-th wheel, from the signal acquired by the eddy current sensor (20) as a function of the calibration curve;F. calculating the lean angle ?by means of the equation: ur)wherein m is the estimated vehicle mass and "u" is a vehicle forward speed estimated by means of an estimation algorithm, and where Fxtis a longitudinal force on the i-th wheel determined from the longitudinal acceleration and the vehicle mass or based on the drive / braking torque on the i-th wheel.

2. A method according to claim 1, wherein the yaw speed of step B is corrected.

3. A method according to claim 1 or 2, wherein the eddy current sensor (20) is inserted into a brake caliper and placed at 2-10mm, preferably at 4-6mm from the brake disc ( 150 ) .

4. A method according to one of claims 1 to 3, wherein two eddy current sensors (20) are used for at least one of the at least one wheel.

5. A system for estimating the operating state conditions of a forward-moving vehicle with at least one wheel provided with a tire and a brake disc (150) , wherein an eddy current sensor (20) coupled to the brake disc (150) and placed at a given distance from the brake disc is used for each of the plurality of wheels, and wherein there are further provided on the vehicle: a steering angle sensor; an accelerometer; a gyro sensor;and wherein an electronic control unit (600) is further included, configured to carry out the steps of the method according to one of claims 1 to 4.

6. A system according to claim 5, wherein the eddy current sensor (20) is inserted into a brake caliper and placed at 2-10mm, preferably at 4-6mm from the brake disc ( 150 ) .

7. A system according to claim 5 or 6, wherein two eddy current sensors (20) are used for at least one of the at least one wheel.

8. A system according to claim 7, wherein the two eddy current sensors (20) are applied to the brake disc (200) at both ends of a diameter of the brake disc, or to the inner and outer sides of the brake disc (100) , or to two brake discs of a same motor vehicle axle.

Images