Method for estimating the temperature of a brake disc, during braking and in off-brake situations

Abstract

The present invention relates to a method (200) for estimating the temperature of a brake disc (150) of a vehicle in driving conditions, wherein the inductive output and the resistive output of an eddy current sensor (20) positioned at a distance between 2 and 10mm from the brake disc (150) are used. The temperature of the eddy current sensor (20) is first estimated (210) based on the resistive output, and if this temperature is less than the Curie temperature of the sensor, a deformation value of the brake disc (150) is firstly determined using the inductive output of the eddy current sensor of step A, and then (240) a temperature of the brake disc (150) is determined based on the deformation measurement and based on the resistive output, using predetermined calibration curves. If instead the temperature of the eddy current sensor is greater than or equal to the Curie temperature of the sensor, the temperature of the brake disc (150) is estimated (250) only based on the resistive output, using further predetermined calibration curves.

Description

[0001] Method for estimating the temperature of a brake disc during braking and in of f-brake situations

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

[0003] Inventors : Leonardo De Novellis , Giulio Calamai

[0004] The present invention relates to a method for estimating the temperature of a brake disc, during braking and in driving conditions without braking .

[0005] Background art

[0006] Known devices for measuring the temperature of a brake disc are infrared sensors ( as in CN114323294A) , thermocouples ( as in CN108930732A) , as well as thermoelements mounted on the brake disc ( as in CN110462249A) .

[0007] Patent document CN113916551A describes the measurement of the disc thermal deformation with displacement sensors and accelerometers , but it does not mention the estimation / measurement of the disc temperature and instead provides a di f ferent sensor for the temperature estimation .

[0008] Patent document CN108825690 describes a smart detection and maintenance system for the brake pads of an automobile . The system comprises a thickness detection unit , an overheating protection unit , a control unit , and a display unit . The thickness detection unit consists o f a distance sensor ; the overheating protection unit comprises a temperature sensor and a cooling system for heat dissipation . The distance sensor and the temperature sensor are connected to the control unit input , respectively, while the cooling system and the display unit are connected to the control unit output , respectively . The brake pad is provided with two mounting holes used to install the distance sensor and temperature sensor, respectively . Such a smart detection and maintenance system for automobile brake pads detects and displays the thickness of the pads in real time, helping the driver to evaluate the wear condition of the pads , determine whether replacement is necessary, detect and display the temperature of the pads in real time , determine whether the temperature is excessive , and activate the cooling system to lower the temperature of the pads in case of overheating, thus ensuring ef fective braking and prolonging the li fe of the pads .

[0009] Furthermore , US2014 / 198824 describes an eddy current sensor which operates in a contactless manner for measuring the temperature on an measuring obj ect or an electrically conductive component , where the measurement is independent from the distance between the sensor and the measuring ob ect / component , where the inherent temperature of the sensor is determined, preferably in the point in which the measuring coil of the sensor is located, and where the influence of the inherent temperature of the sensor or a thermal gradient present on the sensor on the result of the temperature measurement of the measuring obj ect or component is compensated for .

[0010] The need remains for a method for the contactless , indirect measurement of the temperature of a brake disc ( as is the case with thermocouples ) and without the use of optical methods (pyrometers or infrared) , which have disadvantages for the field of application related to high temperatures and the influence of the measurement related to the surface state of the brake disc .

[0011] Object and subject-matter of the invention

[0012] It is the obj ect of the present invention to provide a method for estimating the temperature of a brake disc, during braking and in non-braking situations , which solves the problems and overcomes the drawbacks of the prior art .

[0013] The present invention relates to a method according to the appended claims .

[0014] Detailed description of embodiments of the invention

[0015] List of figures

[0016] The invention will now be described by way of a nonlimiting example , with particular reference to the figures in the accompanying drawings , in which :

[0017] - figure 1 shows , from ( a ) to ( c ) , a diagrammatic and enlarged view of an embodiment of the method of the invention, in which two eddy current sensors are positioned on either side of a car / vehicle axle (but only one sensor is also functional for the method of the invention) to measure the deformations of the brake disc ;

[0018] - figure 2 shows a brake caliper with some elements according to an embodiment of the present invention;

[0019] - figure 3 shows a flow chart of an embodiment of the brake disc temperature estimation method according to the invention;

[0020] - figure 4 shows a flow chart of an embodiment of a calibration method preliminary to the use of the method for estimating the temperature of the brake disc according to the invention;

[0021] - figure 5 shows a test diagram of an embodiment of the method according to the present invention, in the case of trucks ; and

[0022] - figure 6 shows a test diagram of an embodiment of the method according to the present invention in the case of cars .

[0023] It is here speci fied that elements of di fferent embodiments can be combined to provide further embodiments , without restrictions , by respecting the technical concept of the invention, as those skilled in the art will ef fortlessly understand from the description .

[0024] The present description also makes reference to the prior art for the implementation thereof in relation to the detail features not described, e . g . , elements of minor importance usually used in the prior art in solutions of the same type .

[0025] When an element is introduced, it is always understood that there can be " at least one" or "one or more" .

[0026] 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" such elements .

[0027] When listing features in the same sentence or bul let list , one or more of the individual features can be included in the invention without connection with the other features on the list .

[0028] Embodiments

[0029] The invention involves the use of an eddy current sensor ( disc monitoring sensor ) facing a brake disc and placed at a certain distance from the disc . The eddy current sensor consists of a core of ferromagnetic material ( generally ferrite ) about which turns of electrically conductive wire are wound, in a coil-like manner . 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 itsel f 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 the inductance measurement and information concerning the 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 the sensor and the brake disc changes . The resistance measurement refers to the measurement of the electrical resistance of the conducting wire turns wound about the ferromagnetic material of the eddy current sensor. Such a resistance value varies as the temperature changes.

[0030] The inductance measurement is not effective when the eddy current sensor reaches a characteristic temperature of its ferrite core; such a temperature is referred to as the "Curie temperature" TCurie and indicates the point in which the ferrite material loses its ferromagnetic properties. However, this is a reversible effect.

[0031] The innovative feature in the present invention is related to the estimation of the brake disc temperature.

[0032] The Inventors have seen that, during braking, the inductance and resistance measured by the eddy current sensor are correlated with the disc temperature. In order to estimate such a disc temperature, it is possible to measure the inductance and resistance of the system components and obtain the temperature of the brake disc with an appropriate model. The inductance measurement is not effective for a sensor temperature value Tsensor > Tcurie but the measurement of the electrical resistance of the sensor allows measuring slow variations in disc temperature, according to the physics of the system.

[0033] The Inventors have experimentally verified that the sensor reaches the Curie temperature (230-280°C depending on the type of ferrite used) when the brake disc reaches about 650°C depending on the application (car, motorcycle, etc.) .

[0034] The method and device of the invention can be applied to cars, trucks, commercial vehicles, motorcycles, bicycles, and aircrafts. The method is effective if it is applied to the specific sensor described above when coupled to the brake disc at a given position. There is no contact between the sensor and the disc, therefore there is no wear or damage to the sensor due to contact with the brake disc.

[0035] In more detail, the eddy current sensor can be placed inside a brake caliper or held by a device on the chassis of the car / vehicle or on the suspension or wheel hub, motorcycle forks or caliper attachments.

[0036] The inductance can also be measured in various ways, to name a few, e.g., derived from the circuit voltage and current measurement, from the frequency measurement of an RL (resistor-inductor) circuit, or from the frequency measurement of an RLC (resistor-inductor- capacitor) circuit.

[0037] With reference to Fig. 1, in an embodiment of the invention, there is provided an eddy current sensor (disc monitoring sensor) 20 coupled to a brake disc 150 and placed at a certain distance from the disc, in the general front view (a) of a brake caliper 100. The sensor 20 is placed inside a brake caliper 100 or on any other element of the wheel hub (e.g., hub carrier or additional bracket, motorcycle swingarms / motorcycle swingarm caliper support feet) . 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.

[0038] In more detail, the eddy current sensor is placed at 2-10mm, preferably 4-6mm, from the brake disc, and inserted into a brake caliper. The distance to be used is also a function of the different sizes of the sensor actually used.

[0039] The eddy current sensor 20 in Fig. 1 (c) consists of a ferrite core 21 wrapped by a conductive coil 22. The shape of ferrite and the number of turns of the coil affect the produced magnetic field. The protrusion 23 is a connector, while the hole 24 is provided for the passage of motor-frame connection means (e.g., a screw) .

[0040] The sensor 20 is powered by an electronic control unit (not shown) , which can be positioned close to the caliper or on the vehicle chassis. 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.

[0041] The measurement system thus formed can detect (i) disc and sensor temperature variations or (ii) only the eddy current sensor temperature. Correspondingly, these variations can be detected by monitoring the inductance parameter, which is variable as a function of the disc and / or sensor temperature, or the internal resistance parameter of the sensor, which is variable as a function of the eddy current sensor temperature. Hence, a model, appropriately calibrated on such variabilities, can be predicted to provide a disc temperature estimate.

[0042] The inductance can vary with the temperature in relation to the electrical conductivity variations of the materials (disc, electrical conductor of the coil) and to the variations in magnetic permeability of the ferrite. Therefore, the measurement must be temperature compensated for by means of the electrical resistance measurement. The electrical resistance measurement provides the direct measurement of the eddy current sensor temperature, by thermo-resistive effect (the measurement principle is based on thermal resistance, i.e., the electrical resistance of a conducting metal changes linearly with the temperature, according to a known law) . The inductance variation according to temperature is a law known a priori for each specific ferromagnetic material used.

[0043] The electrical resistance variation according to temperature is a law known a priori for the specific material used for the sensor coil.

[0044] Disc wear can be a variation factor of the relative disc-sensor distance, therefore a reset function is provided, according to an aspect of the invention, during the initialization step, so as not to affect the disc temperature measurement: when the vehicle is turned on, following a few disc revolutions, the sensor detects the relative distance from the disc face by means of the inductance signal, updating the disc wear value in the control unit and resetting the inductance value to be used for the disc temperature estimation.

[0045] As long as the sensor temperature value is lower than the sensor ferrite de-magnetization threshold (Tcurie) , the embodiment comprises a step of reading and conditioning the SENSOR INDUCTANCE and RESISTANCE quantities, as well as a coefficient matrix a.

[0046] The relation described above can also be represented by the following formula: BDTE(t) = f Ls(t'),Rs(t'),a') where : o BDTE (Brake-Disc Temperature Estimation) : estimation pattern of the brake disc temperature; o Ls: INDUCTANCE pattern of the coupled sensor and brake disc system; o Rselectrical RESISTANCE pattern of the SENSOR; o a disc temperature estimation model parameter matrix, to be identified by appropriate calibration procedure (Fig. 3) ; o f() mathematical map / relation; o t: time instant.

[0047] Furthermore, the measurement of the electrical resistance of the coil provides a direct measurement of the temperature inside the sensor, and thus of the area at the distance of the sensor from the brake disc.

[0048] When the sensor exceeds the Curie temperature, the only available information related to the disc temperature is obtained from the measurement of the electrical resistance of its coil by means of calibration. Instead, the sensor temperature is obtained by means of the following reduced mathematical formula:

[0049] BDTE(t) = f(Rs(t),a)

[0050] The inductance and resistance measurements at different sensor temperature ranges are joined by means of a specific algorithm to obtain the disc temperature, as shown in Fig. 2. Such an algorithm has been tested on a test bench for passenger cars (Fig. 5) and trucks (Fig. 4) up to a disc temperature of about 800°C.

[0051] In the case in Fig. 5, the superimposition of the estimated disc temperature (curve with squares) and the measured disc temperature (curve with filled dots) is very good, in which case the sensor output in terms of both resistance and inductance measurement are used. In the case in Fig. 4, higher disc temperatures are reached, therefore at a disc temperature of about 600-650°C, where the sensor exceeds 200°C, the inductance signal output (curve with triangles) decreases due to Curie effect, while the resistance signal output (continuous curve) remains valid. The algorithm can use only the resistance signal output from 600°C onward to estimate the disc temperature, with less precision than in the previous case, but still much more accurately than the inductance measurement at such temperatures.

[0052] In other words, the algorithm allows switching from combined inductance and resistance measurement to resistance-only measurement. On the one hand, the algorithm correlates the sensor measurement with the disc temperature ( inductance / resistance -> disc deformation -> disc temperature) , and on the other hand, it selects the most suitable sensor output depending on the situation (inductance or resistance) .

[0053] More precisely, and referring to Fig. 3, the algorithm 200 includes an initialization step 210, in which the sensor measurement is reset to account for the disc wear value by measuring the inductance output when the vehicle is turned on .

[0054] This is followed by step 220 , in which the resistance output of the eddy current sensor is taken to estimate the temperature of the sensor (not of the disc ) . With such a temperature , in step 230 , the current temperature zone is checked against the Curie temperature of the sensor itsel f .

[0055] I f the sensor temperature is less than the Curie temperature , the method goes to step 240 in which the disc temperature is estimated based on the inductance measurement and also based on the resistive output of the sensor, the latter to account for the contribution which comes from the sensor temperature .

[0056] Instead, i f the sensor temperature is higher than the Curie temperature in step 230 , then in step 250 the disc temperature is estimated solely with the resistive output of the sensor . The estimate error in this case is small because the resistive output has a small error at such sensor temperatures .

[0057] The procedure indicated by the diagram in Fig . 4 , which is an analytical model identi fication procedure , is used to identi fy the estimation models represented by the above equations . The method 300 involves collecting at 310 the resistive and inductive outputs from the sensor, as well as a more direct disc temperature measurement used as a reference . The " reference primary" can be a pyrometer or a thermocouple sliding on the disc or pressed inside the disc so that it comes out onto the band of the disc to be measured ( sensor placed partially inside the disc) . The reference cycle must be understood as a test cycle, i.e., a set of braking actions, to be performed on a dynamic test bench and / or vehicle. Type and range of the cycle braking actions are chosen on a case-by-case basis depending on the application. The temperatures are measured with the sensor on the disc and the resistive and inductive outputs of the eddy current sensor during the cycle.

[0058] By means of the collected data, the method proceeds with step 320, i.e., the step of calculating the matrix with the parameters a of the estimation models, i.e., the calculation of the calibration curves for both estimation with resistive output only and estimation with resistive and inductive outputs.

[0059] Finally, in step 330, the correct operation of the algorithm 200 can be further validated and verified with the updated estimation models of the new parameters a already calculated.

[0060] 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.

[0061] Advantages of the invention

[0062] The device and method are effective for measuring / estimating the disc temperature both during braking and non-braking, during wheel rotation. The disc temperature measurement at rest is also possible, but with less accuracy, because only the resistance measurement would be used. Compared to the prior art , the invention is capable of measuring the disc temperature accurately ( + / -40 ° C ) without being in contact with the brake disc . No information regarding accuracy can be found in the prior art . Robustness against extreme temperatures of the disc is also clearly achieved by the invention, the sensor being remote and thus at lower temperatures .

[0063] The measuring principle is also di f ferent from the prior art , resulting in a cost-ef fective solution for automotive applications .

[0064] 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 modi fications and changes without departing from the related scope of protection, as defined by the appended claims .

Claims

CLAIMS1. Method (200) for estimating the temperature of a brake disc (150) of a motor vehicle in driving conditions, comprising the execution of the following steps by an electronic processing unit:A. detecting an inductive output and a resistive output of an eddy current sensor (20) positioned at a distance between 2 and 10 mm from the brake disc (150) ;B. determining (210) the wear of the brake disc (150) based on the inductive output detected when the vehicle is started;C. determining (220) the temperature of the eddy current sensor (20) based on the resistive output detected in step A by thermo-resistance;D. comparing (230) the temperature of the step C eddy current sensor with the Curie temperature of the eddy current sensor;E. in case the temperature of step C eddy current sensor is smaller than the Curie temperature of the eddy current sensor, performing the following sub-steps :- estimating (240) a brake disc temperature (150) on the basis of the inductive output and on the basis of the resistive output, as well as on the basis of the wear of the brake disc (150) as determined in step B, using predetermined calibration curves;F. in case the eddy current sensor temperature ofstep C is greater than or equal to the Curie temperature of the eddy current sensor, performing the following sub-steps:- estimating (250) the brake disc temperature (150) solely on the basis of the resistive output, using further predetermined calibration curves.

2. Method according to claim 1, wherein in step A the inductive output and the resistive output of an eddy current sensor (20) positioned inside a brake caliper (100) are detected.

3. Method according to claim 1 or 2, wherein in step A the eddy current sensor (20) is a first eddy current sensor, a second eddy current sensor being positioned at a distance between 2 and 10mm from the brake disc (150) on the opposite side to the first eddy current sensor, wherein in steps B to E the averages of the inductive and resistive outputs of the first and second eddy current sensors are used.

4. Method according to one of claims 1 to 3, wherein the predetermined calibration curves and the further predetermined calibration curves are determined in a preliminary calibration step (300) , in which the following sub-steps are performed:- acquiring (310) the resistive and inductive outputs from the eddy current sensor (20) , as well as a measurement of the brake disc temperature (150) viaa calibration temperature sensor placed on or partially inside the brake disc (150) ;- performing a test cycle including a series of braking operations with the brake disc (150) and the acquisition of corresponding brake disc temperatures measured via the calibration temperature sensor as well as the acquisition of the resistive and inductive outputs of the eddy current sensor (20) ;- calculating the calibration curves and further calibration curves based on the temperatures and resistive and inductive outputs of the test cycle.

5. Apparatus for estimating the temperature of a brake disc (150) of a motor vehicle in driving conditions, comprising the use of an eddy current sensor (20) positioned at a distance between 2 and 10mm from the brake disc (150) , the system comprising an electronic control unit configured to carry out steps A-E of the method according to one of claims 1 to 4.

6. Apparatus according to claim 5, wherein the electronic control unit is the ECU unit of the motor vehicle .

7. Apparatus according to claim 5 or 6, wherein the eddy current sensor (20) is a first eddy current sensor, positioned at a distance between 2 and 10mm from the brake disc (150) , a second eddy current sensor being used and positioned at a distance between 2 and 10mmfrom the brake disc ( 150 ) on the opposite side to the first eddy current sensor, the electronic control unit using in the method steps averages of the inductive and resistive outputs of the first and second eddy current sensors .8 . Apparatus according to one of claims 5 to 7 , wherein the first eddy current sensor and / or the second eddy current sensor is positioned inside a brake caliper or fixed to a chassis of the motor vehicle .

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