Determination of brake fluid life based on continuous level and quality measurements

Abstract

A vehicle includes a system and method of monitoring a condition of brake fluid. The system includes a first sensor configured to measure a fluid level of the brake fluid within a reservoir, a second sensor configured to measure a concentration of the brake fluid, a third sensor configured to measure a temperature of the brake fluid, and a processor. The processor is configured to estimate the condition of the brake fluid from the fluid level, the concentration, and the temperature and send a signal to a display indicating the condition of the brake fluid.

Description

TECHNICAL FIELD

[0001] The subject disclosure relates to brake fluid used in vehicle brakes, and in particular, a method for determining the remaining life of brake fluid based on continuous fluid level and mass measurements. BACKGROUND

[0002] Braking systems of automobiles or vehicles are used to control and slow the rotation of vehicle wheels. One component of the braking system is a hydraulic operated brake fluid for brake pads. Brake fluid deteriorates over time, reducing the operational performance of the braking system. Current brake fluid sensors only provide an alert when the brake fluid reaches a certain fluid level in its reservoir. Such sensors do not provide a comprehensive knowledge about the remaining usefulness of the brake fluid. Therefore, it is desirable to provide a system and method that can determine the health of the brake fluid at any time during its life. SUMMARY

[0003] In one example embodiment, a method of monitoring a condition of brake fluid is disclosed. A fluid level of the brake fluid within a reservoir is measured at a first sensor. A concentration of the brake fluid is measured at a second sensor. A temperature of the brake fluid is measured at a third sensor. The condition of the brake fluid is estimated from the fluid level, the concentration, and the temperature at a processor. A signal is sent to a display indicating the condition of the brake fluid.

[0004] In addition to one or more of the features described herein, the method includes determining a wear on brake pads based on at least one of the condition of the fluid and a consumption rate of the brake fluid. The condition of the brake fluid is at least one of a remaining useful life of the brake fluid, a presence of water in the brake fluid, a chemical composition of the brake fluid, and an oxidation level of the brake fluid. In the case where the reservoir is disposed on a vehicle, the method further includes applying a filter to the measurement of the fluid level to compensate for motion of the measurement, wherein the filter is based on dynamics of the vehicle. The method further includes comparing the fluid level, the concentration, and the temperature to at least one of simulation data and historical data. The method further includes detecting a replacement of the brake pads from a discontinuity in the fluid level. Measuring the fluid level includes determining a plurality of fluid level measurements obtained over time.

[0005] In another example embodiment, a system for monitoring a condition of brake fluid is disclosed. The system includes a first sensor configured to measure a fluid level of the brake fluid within a reservoir; a second sensor configured to measure a concentration of the brake fluid; a third sensor configured to measure a temperature of the brake fluid; and a processor. The processor is configured to estimate a condition of the brake fluid from the fluid level, the concentration, and the temperature and send a signal to a display indicating the condition of the brake fluid.

[0006] In addition to one or more of the features described herein, the processor is further configured to determine wear on the brake pad based on at least one of a condition of the fluid and a consumption rate of the brake fluid. The condition of the brake fluid is at least one of a remaining useful life of the brake fluid, a presence of water in the brake fluid, a chemical composition of the brake fluid, and an oxidation level of the brake fluid. In the case where the reservoir is disposed on a vehicle, the processor is further configured to apply a filter to the measurement of the fluid level to compensate for a measurement of motion, where the filter is based on dynamics of the vehicle. The processor is further configured to compare the fluid level, concentration, and temperature to at least one of simulation data and historical data. The processor is further configured to detect a replacement of the brake pad from a discontinuity in the fluid level. The first sensor is further configured to measure the fluid level by obtaining a plurality of measurements of the fluid level over time.

[0007] In yet another example embodiment, a vehicle is disclosed. The vehicle includes a reservoir having brake fluid therein, a first sensor configured to measure a fluid level of the brake fluid in the reservoir, a second sensor configured to measure a concentration of the brake fluid, a third sensor configured to measure a temperature of the brake fluid, and a processor. The processor is configured to estimate a condition of the brake fluid from the fluid level, concentration, and temperature and to send a signal to a display indicating the condition of the brake fluid.

[0008] In addition to one or more of the features described herein, the processor is further configured to determine wear on the brake pad based on at least one of a condition of the fluid and a consumption rate of the brake fluid. The condition of the brake fluid is at least one of a remaining useful life of the brake fluid, a presence of water in the brake fluid, a chemical composition of the brake fluid, and an oxidation level of the brake fluid. The processor is further configured to apply a filter to the measurement of the fluid level to compensate for a measurement of motion, where the filter is based on dynamics of the vehicle. The processor is further configured to compare the fluid level, concentration, and temperature to at least one of simulation data and historical data. The processor is further configured to detect a replacement of the brake pad from a discontinuity in the fluid level.

[0009] The above mentioned and other features and advantages of the disclosure will be apparent from the following detailed description, taken in conjunction with the accompanying drawings, illustrating by way of example the principles of the disclosure. BRIEF DESCRIPTION OF DRAWINGS

[0010] Other features, aspects, and details of the application can be described in the following detailed description, and can be apparent from the description or can be learned from practice of the application.

[0011] Figure 1 A vehicle according to an example embodiment is shown;

[0012] Figure 2A schematic diagram of a vehicle braking system in an illustrative embodiment is shown;

[0013] Figure 3 A flowchart illustrating the operation of a brake fluid health monitor of a braking system in an embodiment is shown;

[0014] Figure 4 A schematic diagram of a method for estimating the remaining life of brake fluid is shown;

[0015] Figure 5 A graph illustrating the depletion of normal brake fluid over time is shown;

[0016] Figure 6 A schematic diagram of a method for estimating brake pad wear is shown;

[0017] Figure 7 A graph illustrating the effect of replacing brake pads or other service work on brake fluid level is shown;

[0018] Figure 8 A graph illustrating brake fluid level due to brake pad wear is shown; and

[0019] Figure 9 A graph of a method for determining conditions for replacing brake pads is shown. DETAILED DESCRIPTION

[0020] The following description is merely exemplary in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

[0021] According to exemplary embodiments, Figure 1 A vehicle 100 is shown. The vehicle 100 includes a braking system 102 configured to provide brake torque to one or more wheels 104. In operation, force applied at the braking system 102 is transmitted via brake fluid to brake pads 120 at the one or more wheels 104. As disclosed herein, the braking system 102 also includes sensors for obtaining measurements of brake fluid.

[0022] The vehicle 100 includes vehicle dynamics sensors 106 that obtain measurements of dynamic parameters of the vehicle 100. The vehicle dynamics sensors 106 can refer to a plurality of dynamic sensors. The dynamic parameters can include, but are not limited to, vehicle grade or inclination of the vehicle relative to level, pitch of the vehicle, roll of the vehicle, yaw of the vehicle, longitudinal acceleration of the vehicle, lateral acceleration of the vehicle, and commanded brake torque of the vehicle.

[0023] The vehicle 100 also includes a controller 108 that performs various operations at the vehicle. The brake system 102 and the vehicle dynamics sensors 106 are in communication with the controller 108 and provide their measurements to the controller. The controller 108 includes a processor 110 and a computer-readable storage device or storage medium 112. The storage medium 112 includes programs or instructions 114 that, when executed by the processor 110, allow the processor to estimate the remaining life of the brake fluid based on the measurements obtained from the brake system 102 and from the vehicle dynamics sensors 106. The remaining life estimate can be sent to a display 116 to alert the user that brake pads need to be replaced, brake fluid needs to be replaced, or other maintenance procedures.

[0024] Figure 2 A schematic structure 200 of the brake system 102 in the illustrative embodiment is shown. The brake system 102 includes a reservoir 202 that stores brake fluid 204. The brake fluid 204 forms a meniscus 206 that indicates the fluid level or height of the brake fluid within the reservoir 202. Over time, the brake fluid 204 is depleted due to use of the brakes, causing the level of the meniscus 206 within the reservoir 202 to decrease.

[0025] A fluid level sensor 210 (first sensor) is coupled to the reservoir 202 and measures the fluid level of the brake fluid 204 within the reservoir 202. The fluid level sensor 210 is a continuous sensor. In other words, the fluid level sensor 210 measures the fluid level at any height within the fluid level range of the reservoir 202. The measurements can be obtained multiple times. A fluid quality sensor 212 (second sensor) is also coupled to the reservoir 202. The fluid quality sensor 212 measures the concentration or chemical composition of the brake fluid 204. For example, the fluid quality sensor 212 can detect the amount of foreign fluids (such as water or other contaminants) in the brake fluid 204. In addition, the fluid quality sensor 212 can measure the amount of oxidation in the brake fluid 204 in the reservoir 202. Oxidation of the brake fluid indicates degradation of the brake fluid. The presence of oxidized brake fluid decreases the boiling point of the brake fluid. The concentration of the brake fluid 204 can therefore be used to determine the amount of contamination or degradation of the brake fluid. The fluid quality sensor 212 is capable of making concentration measurements at any selected time. A temperature sensor 214 (third sensor) is coupled to the reservoir 202 and is capable of measuring the temperature of the brake fluid 204 at any selected time. Knowing the temperature of the brake fluid 204 in conjunction with the concentration measurements allows one to determine the overall quality of the fluid at a certain moment in time. For example, the presence of water in the brake fluid 204 at low temperatures (due to its hygroscopic nature) changes the viscosity of the brake fluid and therefore affects the sloshing behavior.

[0026] Figure 3The process 300 is shown, which illustrates the operation of the brake fluid health monitor in an embodiment. In block 302, measurements of fluid level (by fluid level sensor 210), concentration of brake fluid 204 (by fluid mass sensor 212), and brake fluid temperature (by temperature sensor 214) are obtained. In block 304, the measurements are used to estimate the remaining life of brake fluid 204. In block 306, the measurements are used to estimate the remaining life of brake pads 120.

[0027] Figure 4 The process 400 is shown for a method of estimating the remaining life of brake fluid 204. The method includes determining the health state of brake fluid 204 from measurements taken at vehicle 100, including measurements from fluid level sensor 210, fluid mass sensor 212, fluid temperature sensor 214, and dynamic parameters obtained from vehicle dynamics sensor 106.

[0028] In block 402, a time measurement of fluid level of brake fluid 204 is obtained. In block 404, the concentration / mass of brake fluid is measured. In block 406, brake fluid compatibility is determined from brake fluid concentration and brake fluid mass. The concentration sensor determines whether the medium filling the brake system is actually brake fluid based on calibration to the correct brake fluid concentration. Based on the fluid concentration measurement, it can be determined whether the correct type of brake fluid has been added to reservoir 202. For example, if a foreign or unexpected fluid (e.g., an incompatible type of brake fluid, other automotive fluid, or water) is detected by the mass sensor in reservoir 202, it is important to flag the data (block 406) before sending the data for the brake fluid health monitoring algorithm (block 410). In block 408, a temperature measurement is obtained from temperature sensor 214.

[0029] In block 410, the processor estimates the brake fluid condition from blocks 402, 404, and 408. The estimation of the brake fluid condition can be based on a comparison of the brake fluid level, fluid concentration, and temperature to data obtained from simulations (block 412) and / or historical data (block 414). In block 412, a simulation is performed that determines normal fluid mass degradation using a model. The measurements of blocks 402, 404, and 408 can be compared to the simulation data to estimate the brake fluid condition. Block 414 includes historical data from other field measurements. The measurements of blocks 402, 404, and 408 can be compared to the historical data to estimate the brake fluid condition. In addition, the measurements of blocks 402, 404, and 408 can be stored as historical data for future calculations.

[0030] In block 416, a signal can be sent (e.g., to the display 116) to indicate that the brake fluid is incompatible with the vehicle 100 and that the vehicle should be serviced and the brake fluid replaced based on the estimated brake fluid condition. In block 418, the estimate of the brake fluid condition can be used to estimate the remaining life of the brake fluid. The remaining life can be quantified in various dimensions, such as remaining distance (e.g., in kilometers), percentage, and / or remaining time.

[0031] Figure 5 A relationship 500 is shown that illustrates the consumption of normal brake fluid over time. Time (T) is shown along the horizontal axis and brake fluid level (h) is shown along the vertical axis. Time is typically shown in a "long" time frame, such as months or years. Data points 502 represent the fluid level at different times. A regression line 504 is determined for the data points 502 and a minimum boundary 506 and a maximum boundary 508 are established for the data points 502. The minimum boundary 506 can be a deviation downward from the regression line 504, such as one or two standard deviations. Similarly, the maximum boundary 508 can be a deviation upward from the regression line 504, such as the same one or two standard deviations. The minimum boundary 506 and the maximum boundary 508 can be used to establish a range of normal brake fluid consumption for the brake system 102.

[0032] Figure 6 A flow 600 for a method of estimating brake pad wear is shown. In block 602, dynamic parameters of the vehicle are obtained. The dynamic parameters include vehicle grade or inclination, pitch, roll, yaw of the vehicle, lateral / longitudinal acceleration, and brake torque. Vehicle grade is the angular deviation of the vehicle from the horizontal, representing the angle of inclination of the meniscus of fluid in the brake fluid reservoir. Similarly, lateral and longitudinal acceleration, pitch, roll, yaw, and brake torque of the vehicle are related to the perturbed level of fluid in the brake fluid reservoir.

[0033] In block 604, the brake fluid level in the brake fluid reservoir is measured. The brake fluid level is either a continuous measurement or a plurality of measurements obtained over time, or both.

[0034] In block 606, a sloshing filter is applied to the brake fluid level measurements obtained in block 604. The sloshing filter is based on the dynamic vehicle parameters obtained in block 602. The sloshing filter outputs an adjusted brake fluid level that corrects the fluid level measurements for vehicle dynamic motion. Table 1 illustrates a decision method for the sloshing filter in an illustrative embodiment.

[0035] Table 1

[0036]

[0037] In the first row, the vehicle grade or inclination is determined and, if above a threshold, is used to correct the fluid level measurement. In the second row, lateral and / or longitudinal acceleration of the vehicle is measured. The fluid level is corrected to account for the effect of lateral and / or longitudinal acceleration on the fluid level measurement. In the third row, the commanded brake torque is measured. If the commanded brake torque is greater than or close to zero, the warning filter anticipates that the brake fluid will slosh and compensates for the sloshing in the fluid level measurement.

[0038] The test results obtained using Table 1 are used to generate a slosh detection flag that indicates whether any amount of brake fluid 204 in the reservoir 202 is sloshing. In an embodiment, if the results of the slosh filter indicate that sloshing is expected, the measurement data points (i.e., fluid level, etc.) can be recorded as historical data without requiring any immediate control changes based on the status of the brake fluid condition.

[0039] Block 608 includes a model that simulates normal brake pad wear over time given various usage scenarios. Block 610 includes historical data of brake pad wear of the brake pad 120 given usage time. Block 612 receives the continuous fluid level measurements from block 604, the filtered brake fluid level from block 604, the simulated data from block 608, and the historical data from block 610, and estimates the amount of brake wear based on a comparison of the measurements to the simulated data or the historical data or both.

[0040] Figure 7 A relationship 700 is shown that illustrates the effect of replacing brake pads or other maintenance work on the brake fluid level. Time (T) is shown along the horizontal axis and brake fluid level (h) is shown along the vertical axis. Time is generally shown over a "long" time frame, such as months or years. Brake pad replacement occurs at time to. Accordingly, a discontinuity 702 occurs at time to in the regression line 704 as well as the minimum boundary line 706 and the maximum boundary line 708. The discontinuity can be due to refilling of brake fluid during replacement of the brake pads. The processor 110 can identify the discontinuity, and the processor 110 can make adjustments so as to provide consistent measurements of brake fluid level and consumption rate.

[0041] Figure 8A relationship 800 is shown that illustrates brake fluid level due to brake pad wear. Time (T) is shown along the horizontal axis and brake fluid level (h) is shown along the vertical axis. Time is generally shown in a "short" time frame. Fluid level measurements 802 are obtained over a plurality of drive cycles 804. A minimum boundary line 806 indicates an expected minimum fluid level for normal pad wear and a maximum boundary line 808 indicates an expected maximum fluid level for normal pad wear. A lower deviation line 810 indicates an expected minimum data measurement range due to brake pad wear and an upper deviation line 812 indicates an expected maximum data measurement range due to brake pad wear. Fluid level decreases over time due to pad wear. A rate of consumption can be determined from the relationship 800 and used to indicate an amount of wear on the brake pads 120.

[0042] Figure 9 A flowchart 900 of a method for determining a condition for replacing the brake pads 120 is shown. In block 902, continuous measurements of brake fluid level are obtained. In block 904, brake pad wear is estimated based on fluid level correlations. In block 906, brake pad wear is estimated using a brake wear simulation model. In block 908, an indication that the brake pads 120 need to be replaced is made from information from blocks 902, 904, and 906.

[0043] While the foregoing disclosure has been described in reference to exemplary embodiments, it will be understood by those skilled in the art that various changes can be made and equivalents can be substituted for elements thereof without departing from the scope thereof. In addition, many modifications can be made to adapt a particular situation or material to the teachings of the disclosure without departing from the essential scope thereof. Therefore, the disclosure is not limited to the particular embodiments disclosed, but will include all embodiments falling within the scope of the disclosure.

Claims

1. A method for monitoring the condition of brake fluid, comprising: The fluid level of the brake fluid in the reservoir is measured at the first sensor. The concentration of the brake fluid is measured at the second sensor; The temperature of the brake fluid is measured at the third sensor; At the processor, the condition of the braking fluid is estimated by comparing the fluid level, concentration, and temperature with at least one of the simulation data and historical data based on the amount of contamination or deterioration of the fluid mass. A signal is displayed on the screen indicating the status of the brake fluid. The remaining service life of the brake fluid is determined based on its condition. and The brake fluid will be replenished based on the remaining service life.

2. The method of claim 1, further comprising determining wear on the brake pads based on at least one of: (i) the condition of the fluid; (ii) the rate of consumption of the brake fluid.

3. The method according to claim 1, wherein, The reservoir is mounted on the vehicle and also includes a filter applied to the measurement of the fluid level to compensate for the measurement of motion, wherein the filter is based on the vehicle's dynamics.

4. The method according to claim 1, further comprising detecting brake pad replacement based on discontinuities in the fluid level.

5. The method according to claim 1, wherein, Measuring the fluid level includes determining multiple measurements of the fluid level as it changes over time.

6. A system for monitoring the condition of brake fluid, comprising: A first sensor is configured to measure the fluid level of the brake fluid within the reservoir; A second sensor is configured to measure the concentration of the brake fluid; A third sensor is configured to measure the temperature of the brake fluid; The processor is configured to estimate the condition of the braking fluid by comparing fluid level, concentration, and temperature with at least one of simulation data and historical data based on the amount of contamination or deterioration of the fluid mass. A signal is sent to the display indicating the status of the brake fluid. The remaining service life of the brake fluid is determined based on its condition. and The brake fluid will be replenished based on the remaining service life.

7. The system according to claim 6, wherein, The processor is also configured to determine wear on the brake pads based on at least one of the following: (i) the condition of the fluid; (ii) the rate of consumption of the brake fluid.

8. The system according to claim 6, wherein, The reservoir is mounted on the vehicle, and the processor is further configured to apply a filter to the measurement of the fluid level to compensate for the measurement of motion, wherein the filter is based on the vehicle's dynamics.

9. The system according to claim 6, wherein, The processor is also configured to detect brake pad replacement from discontinuities in the fluid level.

10. The system according to claim 6, wherein, The first sensor is also configured to measure the fluid level by acquiring multiple measurements of the fluid level as it changes over time.

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