Method for continuously measuring brake pad wear and related braking system

Abstract

The present invention relates to a method for continuously measuring wear of the brake pads of a wheeled vehicle comprising a brake caliper (100), a brake disc (150), a brake pad (60) including a friction material (61), wherein the following steps are carried out : providing a first eddy current temperature sensor (20) in the brake caliper (100), placed at a predetermined distance from the brake disc (150); providing a second temperature sensor (65) in said brake pad (60); measuring a first temperature T1 during a braking action of the wheeled vehicle, by means of the first eddy current temperature sensor (20); measuring a second temperature T2 during the braking action of the wheeled vehicle, by means of the second temperature sensor (65); comparing the temperature difference MD=T2-T1 with a look-up table that relates the temperature difference MD to the thickness of the friction material (61); calculating a current thickness S of the friction material (61) based on the comparison of the previous step. The invention also relates to a braking system which implements the method of the invention.

Description

[0001] Method for continuously measuring brake pad wear and related braking system

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

[0003] Inventors : Leonardo De Novellis , Alfonso Tarantini,

[0004] Andrea Milanesi

[0005] The present invention relates to a method for continuously measuring brake pad wear and related braking system.

[0006] Background art

[0007] The continuous measurement of brake pad wear using an inductive (eddy current ) sensor is described in a first set of patent s , CN109715971A and CN109906322A . W02018023104A1 and W02018023104A1 suggest the use of magnetic sensors , with Wi-Fi or integrated into the tire pressure sensor .

[0008] However, these patent documents suggest solutions which are complicated, expensive and difficult to implement , not least having low resistance to high disc temperatures , which could compromise the correct operation of the magnetic sensors .

[0009] Another set of patents , such as S2015152931A1 , W02020202102A1, EP0345208A1 , provide for the use of erodible sensors with additional material placed on the brake pad / material . Such solutions provide an estimate of wear of a brake pad portion which is not sufficiently reliable due to such an erosion .

[0010] Moreover, WO2018 / 022615 describes a brake pad wear measurement system intended for use in a disc brake system with floating caliper, including a piston which supports an inner brake pad and a floating caliper which supports an outer brake pad . The piston and the floating caliper move toward each other along a braking axis in response to the actuation of the braking system, so that the brake pads come into contact and apply a braking force to the brake rotor . The brake pad wear detection system comprises a sensor mounted on the floating caliper and movable therewith along the braking axis , and an actuator mounted so that it moves with the piston along the braking axis . The sensor and the actuator approach each other in response to the actuation of the braking system . The approach distance between the sensor and the actuator in response to the braking system actuation increases by an amount equal to the total wear of the inner and outer brake pads . The sensor detect s the presence of the actuator to provide a signal indicative of brake pad wear .

[0011] Furthermore, US2014 / 198824 describes an eddy-current sensor which operates without contact for measuring the temperature on an measuring object or an electrically conductive component , where the measurement is independent of the distance between the sensor and the measuring object / 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 object or component is compensated for .

[0012] Overall, such solutions cannot continuously measure the brake pad wear in a sufficiently practical and effective manner .

[0013] Object and subject-matter of the invention

[0014] It is an object of the present invention to provide a method for continuously measuring brake pad wear, which solves the problems and overcomes the drawbacks of the prior art .

[0015] It is further the object of the present invention to provide a braking system which implements the method of the invention .

[0016] The present invention relates to a method and a braking system according to the appended claims .

[0017] Detailed description of embodiments of the invention

[0018] List of figures

[0019] The invention will now be described by way of a nonlimiting example, with particular reference to the figures in the accompanying drawings , in which :

[0020] - 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 (motor) vehicle brake disc (but only one sensor is also functional for the method of the invention) , in order to measure the deformations of the brake disc; - figure 2 shows a brake caliper with some elements according to an embodiment of the present invention;

[0021] - figure 3 shows a brake disc and brake pad arrangement diagram according to an aspect of the invention;

[0022] - figure 4 shows a graph of the temperature of the metal pad backplate (also referred to as a "plate" ) and of the surface of the brake disc as a function of the pad thickness ;

[0023] - figure 5 shows the trend of the difference between the two temperatures in Fig . 4 ; and

[0024] - figure 6 shows the temperatures at different brake disc and brake pad depths as a function of the braking time ( cycles ) .

[0025] It is here specified that elements of different 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 effortlessly understand from the description .

[0026] 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 .

[0027] When an element is introduced, it is always understood that there can be "at least one" or "one or more" .

[0028] 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 .

[0029] When listing features in the same sentence or bullet list , one or more of the single features can be included in the invention without connection with the other features on the list .

[0030] Two or more of the parts (elements , devices , systems ) described above can be freely associated and considered as part kits according to the invention .

[0031] Embodiment s

[0032] An embodiment of the invention is an eddy-current temperature sensor inserted into a brake caliper and placed, for example, about 5 mm from the brake disc . Different distances from the brake disc can be considered with different sensor sizes .

[0033] The sensor normally consists of a ferrite core wrapped by a conductive coil . It is powered by an electronic control unit , which can be positioned close to the caliper or on the vehicle chassis . During the operation of the brake, the sensor can measure the disc deformation by measuring the eddy current inductance : the higher the temperature of the disc, the greater its deformation .

[0034] 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 ) . It is also possible to position a temperature sensor 30 inside the brake caliper 100 . It is also possible to place 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 .

[0035] 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 sizes of the sensor actually used .

[0036] The eddy current sensor 20 in Fig . 1 ( c) consists of a ferrite core 21 wrapped 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 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 additional embodiments of the invention .

[0037] During brake operation, the sensor can measure the disc deformation by measuring the eddy current inductance : the greater the deformation of the disc, the higher its temperature . In other words , the measurement of the disc deformation by inductance provides an indirect measure of its temperature . This is achieved by means of a calibration curve in a control unit , e . g . , in the ECU software . This embodiment provides for the presence of an additional temperature sensor inserted into the brake or backplate material (which is absent in some vehicles such as racing vehicles , for example, the pad being monomaterial ( carbon) ) : such a sensor can be any of the temperature sensors available on the market .

[0038] The availability of wear maps installed in the control unit of the vehicle is also considered : these maps allow calculating the extent of pad wear by having only the disc temperature ( 1 st measurement ) and the backplate temperature ( 2nd measurement ) as inputs . Such a sensor is diagrammatically shown in Fig . 2 with reference numeral 65 and is preferably placed on the backplate 62 , with respect to the brake pad 60 . Since the backplate is not always present on a wheeled vehicle, the sensor 65 can generally be placed in the brake pad, e . g . , in the friction material 61 . The eddy current sensor 20 is also shown in the figure .

[0039] The second temperature sensor 65 can be chosen from the group comprising : negative temperature coefficient thermistors , temperature sensors with positive temperature coefficient , thermal resistors , resistors , strain gages , optical fibers , thermocouples . Each of these sensors is suitable for the purpose .

[0040] The mutual situation of the brake pad and the brake disc, showing the measurement points for the tests explained below, is diagrammatically summarized in Fig . 3 . The brake pad 60 comprises a friction material 61 and a plate 62 to which such a friction material is applied . Points A and B, also shown in Fig . 6, are defined on the friction material. The temperature measurement points C and D, also shown in Fig. 6 below, are defined on the brake disc 150 (the rotation axis of which is R) .

[0041] A temperature (1st measurement, Tl) is the disc temperature (measured by the eddy current sensor) which is to be considered equal to or at least very close to (±5%) the temperature of the pad surface in contact with the disc during braking. The second temperature (2nd measurement, T2) is the temperature of the rear plate (backplate) of the brake pad measured by an NTC (negative temperature coefficient thermistor) , PTC (positive temperature coefficient thermistor) or thermocouple (or other sensor listed above) . The use of other sensors / systems for temperature measurement (printed resistor, pyrometers, etc.) is possible.

[0042] If Tl is close to T2, it means that the thickness of the friction material in the middle (between the disc surface and the plate 62) has reduced, i.e., the pad is wearing out .

[0043] By using diagrams like that in Figs. 2-3, it is possible to obtain a better estimate of the thickness of the pad. The greater the temperature difference MD = Tl- T2, the better the estimate. This means that the disc temperature must be sufficiently high to estimate the pad thickness correctly, and this is not common in the average use of a motorcar. It is more likely to happen in motorcycle applications.

[0044] The inventors performed simulations considering the WLTP (Worldwide Harmonized Light Vehicle Test Procedure) and AMS (Auto Motor Sport) cycles: - With three different car models Model 1 , Model 2 and Model 3 , WLTP cycle, MD = 40 ° C with pad at full thickness , MD = 4 ° C with worn pad and pad friction material thickness of 3 mm;

[0045] - For Model 2 and Model 3 , AMS cycle, MD = 250 ° C with pad at full thickness , MD = 50 ° C with pad friction material thickness— of 3 mm .

[0046] These results show that wear can be estimated from the temperature difference between the rear plate and the pad surface .

[0047] Once the temperature difference MD is calculated, a multiplier K obtained from appropriate data tables (" look-up tables" ) is applied thereto to obtain the brake pad thickness S=K«MD .

[0048] The invention relates to a computer program comprising instructions which, when executed on the electronic control unit of the described braking system, cause the execution of the steps of acquiring data from the sensors 20 , 65 and calculating the current thickness of the friction material 61 as shown .

[0049] For practical implementation, the effectiveness of the method for high-energy cycles is apparent . Indeed, figure 6 shows the disc temperature and pad temperature progression as a function of thickness and as the number of braking actions during an AMS test progresses . The figure is obtained by means of a thermo-mechanical simulation of a system mounted on a D-segment vehicle . Specifically, this is a system mounted on the front axle with a brake disc having a thickness of 24 . 5 mm, fixed calipers , and pads with friction material having a thickness of 9 mm when new .

[0050] It is well noted that during the test , instant 94 s, the point A of the pad ( see Fig . 3 ) , in contact with the coordinate point C of the disc, and the point C itself take the same temperature ; in particular, at the end of the test , instant 94 s , the two points have the temperature of 606 ° C . Conversely, the coordinate point B of the pad, which is the one in contact with the plate, tends to take a significantly lower temperature during the test than the coordinate point A, in particular 350 ° C at the end of the test . This simulation was carried out for the case of new, full-thickness pads .

[0051] For low energy cycles , such as WLTP , the accuracy of the measurement should be considered and defined . The method should be applied with wear maps / search tables implemented in the ECU of the vehicle that have disc temperature (eddy current sensor measurement ) as the main input .

[0052] For motorcycles and trucks , no simulation tool is available, but the disc temperatures are higher and therefore the applicability of the method is ensured .

[0053] The present invention is applicable to wheeled vehicles , such as four-wheeled automobiles , for example, and in particular to two-wheeled vehicles such as motorcycles and bicycles .

[0054] Advantages of the invention

[0055] This invention extends the normal warning mechanism in case of brake pad wear . The advantage of this method is that it can provide an intermediate (and continuous ) estimate in addition to the fully worn pad warning .

[0056] Furthermore, this invention could help estimate the emissions of the braking system to which the invention is applied by virtue of continuous pad wear monitoring .

[0057] Compared to patent documents CN109715971A, CN109906322A, W02018023104A1 , and W02018023104A1 , the suggested invention is simple, cost-effective, easy to implement , and resistant to high disc temperature (which could compromise the proper operation of the magnetic sensors ) .

[0058] As for patent documents US2015152931A1 , W02020202102A1 , EP0345208A1 , the present invention does not involve the erosion of additional material placed on the pad / brake material ; furthermore, the second set of patents provides an estimate of wear of a brake pad portion; by means of the present invention, a better estimate of average wear of the brake pad is possible .

[0059] 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. Method for continuously measuring brake pad (60) wear of a wheeled vehicle comprising at least a brake caliper (100) , at least a brake disc (150) , at least a brake pad (60) including a friction material (61) , wherein the following steps are performed:— providing a first eddy current temperature sensor(20) in the brake caliper (100) , placed at a predetermined distance from the brake disc (150) ;— providing a second temperature sensor (65) in said brake pad (60) ;— measuring a first temperature T1 during braking of the wheeled vehicle, by the at least a first eddy current temperature sensor (20) ;— measuring a second temperature T2 during braking of the wheeled vehicle, by the at least a second temperature sensor (65) ;— comparing the temperature difference MD=T2-T1 with a look-up table that relates the temperature difference MD to the thickness of the friction material (61) ;— calculating a current thickness S of the friction material (61) based on the comparison of the previous step.

2. Method according to claim 1, wherein the at least a second temperature sensor (65) is provided in the friction material (61) .

3. Method according to claim 1, wherein the brake pad (60) includes a backplate (62) and the at least a second temperature sensor (65) is provided on the backplate (62) .

4. Method according to any one claim 1-3, wherein the predetermined distance is 2-10 mm.

5. Method according to claim 2, wherein the predetermined distance is 4-6 mm.

6. Method according to any one claim 1-5, wherein the at least a second temperature sensor (65) is chosen in the group comprising: negative temperature coefficient thermistors, temperature sensors with positive temperature coefficient, thermo-resistors, resistors, strain gauges, optical fibers, thermocouples.

7. Wheeled vehicle braking system comprising at least a brake caliper (100) , at least a brake disc (150) , at least a brake pad (60) which includes a friction material (61) , as well as an electronic control unit, characterized by further comprising:— at least a first eddy current temperature sensor (20) inserted in the at least a brake caliper (100) and placed at a predetermined distance from the at least a brake disc (150) ;- at least a second temperature sensor (65) installed in said brake pad (60) ; wherein the at least a first (20) and the at least asecond (65) temperature sensors are connected to said electronic control unit, which includes electronic means configured for:A. acquiring from the at least a first eddy current temperature sensor (20) a first temperature T1 during a braking of the wheeled vehicle;B. acquiring from the at least a second temperature sensor (65) a second temperature T2 during a braking of the wheeled vehicle;C. comparing the temperature difference MD=T2-T1 with a look-up table relating the temperature difference MD to the thickness of the friction material (61) ;D. calculating a current thickness S of the friction material (61) based on said comparison.

8. System according to claim 7, wherein the at least a second temperature sensor (65) is provided in the friction material (61) .

9. System according to claim 7, wherein the at least a brake pad (60) includes a backplate (62) and the at least a second temperature sensor (65) is provided on the backplate (62) .

10. System according to any one claim 7-9, wherein the predetermined distance is 2-10 mm.

11. System according to claim 10, wherein the predetermined distance is 4-6 mm.

12. System according to any one claim 7-11, wherein the at least second temperature sensor (65) is chosen from the group comprising: negative temperature coefficient thermistors, positive temperature coefficient temperature sensors, thermo-resistors, resistors, strain gauges, optical fibers, thermocouples.

13. System according to any one claim 7 to 12, wherein said wheeled vehicle is chosen in the group comprising: car, motorcycle, bicycle.

14. Computer program comprising instructions which, when executed on the electronic control unit of the system of one of claims 7 to 13, cause the execution of said steps A to D .

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