Patent Grant
11867246
The present disclosure claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2020-128562, filed Jul. 29, 2020, the contents of which application are incorporated herein by reference in their entirety.
The present disclosure relates to a technique of estimating a wear volume of a brake pad of a vehicle.
Japanese Patent No. 6207075 a wear volume computation device that calculates a wear volume of a braking member of a railroad car and the like. The wear volume computation device calculates (estimates) the wear volume of the braking member based on a brake pressure, a speed of a braking target, and a braking time.
During braking of a vehicle, a braking force is generated by pressing a brake pad against a brake rotor rotating with a wheel. At this time, the brake pad is worn by friction between the brake pad and the brake rotor. A wear volume of the brake pad per unit input (i.e., per single braking) basically depends on a vehicle speed, a brake pressure, and a brake duration.
The inventor of this application pays attention to a change in physical property of the brake pad due to heat. During braking of the vehicle, frictional heat is generated due to the friction between the brake pad and the brake rotor. Due to the frictional heat, the physical property of a material of the brake pad irreversibly changes, and thus wear characteristics of the brake pad change. Such the change in wear characteristics of the brake pad due to heat is not considered in Japanese Patent No. 6207075. In the case where the change in wear characteristics of the brake pad due to heat is not considered, an estimation accuracy of the wear volume is decreased.
An object of the present disclosure is to provide a technique that can increase an estimation accuracy of a wear volume of a brake pad of a vehicle.
A first aspect is directed to a wear volume estimation device that estimates a wear volume of a brake pad of a vehicle.
The wear volume estimation device includes:
The processor is programmed to execute:
In the wear volume calculation process, the processor variably sets the wear volume function according to the temperature history of the contact surface indicated by the temperature history information acquired at a time of previous braking.
A second aspect is directed to a wear volume estimation method that estimates a wear volume of a brake pad of a vehicle.
A wear volume function expresses the wear volume as a function of a vehicle speed, a brake pressure, and a brake duration.
The wear volume estimation method includes:
The wear volume calculation process includes a process of variably setting the wear volume function according to the temperature history of the contact surface indicated by the temperature history information acquired at a time of previous braking.
A third aspect is directed to a wear volume estimation program that estimates a wear volume of a brake pad of a vehicle.
A wear volume function expresses the wear volume as a function of a vehicle speed, a brake pressure, and a brake duration.
The wear volume estimation program, when executed by a computer, causes the computer to execute:
The wear volume calculation process includes a process of variably setting the wear volume function according to the temperature history of the contact surface indicated by the temperature history information acquired at a time of previous braking.
According to the present disclosure, the temperature of the contact surface of the brake pad that comes in contact with the brake rotor is estimated during the braking of the vehicle. Then, the temperature history information indicating the temperature history of the contact surface is updated based on the temperature of the contact surface. When calculating the wear volume of the brake pad, the temperature history of the contact surface indicated by the temperature history information is taken into consideration. More specifically, the wear volume function used for calculating the wear volume of the brake pad is not fixed but variably set according to the temperature history of the contact surface. As a result, the estimation accuracy of the wear volume is improved.
Embodiments of the present disclosure will be described below with reference to the attached drawings.
The brake rotor 20 is a rotatable member that rotates with the wheel 5. For example, a material of the brake rotor 20 is cast iron. The brake pad 30 is a friction material that comes in contact with the brake rotor 20. For example, the brake pad 30 is formed by baking and solidifying a composite material including various organic fibers and inorganic fibers with a resin.
The actuator 40 moves and presses the brake pad 30 against the brake rotor 20 in response to the brake operation by the driver or the automated driving system. More specifically, the actuator 40 generates a brake pressure Pb in response to the brake operation and presses the brake pad 30 against the brake rotor 20 by the brake pressure Pb. For example, the actuator 40 includes a master cylinder and a caliper. In response to the brake operation, the master cylinder pushes brake fluid out to the caliper to generate the brake pressure (brake fluid pressure) Pb. The brake pressure Pb causes a piston in the caliper to push the brake pad 30 and push it against the brake rotor 20. As a result, the braking force is generated.
A brake pressure sensor 51 detects the brake pressure (brake fluid pressure) Pb.
During braking of the vehicle 1, the braking force is generated by pressing the brake pad 30 against the brake rotor 20 rotating with the wheel 5. At this time, a surface of the brake rotor 20 and a surface of the brake pad 30 come in contact with each other. The surface of the brake rotor 20 that comes in contact with the brake pad 30 is hereinafter referred to as a “contact surface 21.” Similarly, the surface of the brake pad 30 that comes in contact with the brake rotor 20 is hereinafter referred to as a “contact surface 31.” Due to friction between the contact surface 21 and the contact surface 31, the contact surface 31 of the brake pad 30 is worn. Hereinafter, a method of estimating a wear volume of the brake pad 30 will be described.
A wear volume W of the brake pad 30 per unit of input (i.e., per single braking) depends on a vehicle speed V, the brake pressure Pb, and a brake duration tb. The vehicle speed V is a rotational speed of the wheel 5 (i.e., a wheel speed). The brake duration tb is a duration in which the brake pressure Pb (i.e., the braking force) is generated. The wear volume W increases as the vehicle speed V becomes higher. The wear volume W increases as the brake pressure Pb becomes higher. The wear volume W increases as the brake duration tb becomes longer. That is, the wear volume W is expressed by the following Equation (1).
W=f(V,Pb,tb) Equation (1):
A wear volume function f expresses the wear volume W as a function of the vehicle speed V, the brake pressure Pb, and the brake duration tb. The wear volume function f is a formula or a map designed in advance. The wear volume function f is designed so that the wear volume W increases as the vehicle speed V becomes higher. Similarly, the wear volume function f is designed so that the wear volume W increases as the brake pressure Pb becomes higher. In addition, the wear volume function f is designed so that the wear volume W increases as the brake duration tb becomes longer.
A wear volume estimation device 100 shown in
The wear volume estimation device 100 calculates (estimates) the wear volume W for each brake operation. The wear volume estimation device 100 may calculate a cumulative wear volume Wt by integrating the wear volume W calculated for each brake operation. If the cumulative wear volume Wt exceeds a threshold, the wear volume estimation device 100 may output an alert through an output device 60 (e.g., a display, a speaker).
Typically, the wear volume estimation device 100 is installed on the vehicle 1. Alternatively, the wear volume estimation device 100 may be placed outside the vehicle 1 and remotely estimate the wear volume W. In this case, the wear volume estimation device 100 communicates with the vehicle 1 to acquire the information detected by the sensor 50 installed on the vehicle 1.
Wear characteristics of the heat-denatured portion 33 are different from wear characteristics before the heat denaturation. For example, when the brake pad 30 includes a resin, the resin decomposes, melts, and vaporizes at a high temperature condition. As a result, the heat-denatured portion 33 becomes brittle and easy to shave. That is, the heat-denatured portion 33 is more easily worn as compared with the case before the heat denaturation. If such the change in wear characteristics due to head is not considered, an estimation accuracy of the wear volume W is decreased.
In view of the above, according to the present embodiment, the wear volume estimation device 100 estimates the wear volume W in consideration of a temperature history of the brake pad 30 (the contact surface 31) as well. More specifically, during the braking of the vehicle 1, the wear volume estimation device 100 estimates a temperature of the contact surface 31 of the brake pad 30 and updates the temperature history of the contact surface 31 based on the estimated temperature. At a time of next braking, the wear volume estimation device 100 calculates the wear volume W by variably setting the wear volume function f according to the temperature history of the contact surface 31. In other words, the wear volume estimation device 100 calculates the wear volume W by using the wear volume function f that is set according to the temperature history of the contact surface 31.
As shown in
According to the present embodiment, as described above, the wear volume function f used for calculating the wear volume W is not fixed but variably set according to the temperature history of the contact surface 31 of the brake pad 30. As a result, the estimation accuracy of the wear volume W is improved.
Hereinafter, the wear volume estimation device 100 according to the present embodiment will be described in more detail.
The wear volume estimation device 100 may be included in an ECU (Electronic Control Unit) that controls the vehicle 1.
A wear volume estimation program 200 is a computer program executed by a computer. The functions of the wear volume estimation device 100 (the processor 101) is implemented by the processor 101 executing the wear volume estimation program 200. The wear volume estimation program 200 is stored in the storage device 102. The wear volume estimation program 200 may be recorded on a computer-readable recording medium. The wear volume estimation program 200 may be provided through a network.
Sensor detection information 300 is information detected by the sensor 50 installed on the vehicle 1. The sensor 50 includes the brake pressure sensor 51 and a wheel speed sensor 52. The brake pressure sensor 51 detects the brake pressure Pb. The wheel speed sensor 52 detects the vehicle speed V. The sensor detection information 300 includes the vehicle speed V, the brake pressure Pb, and the brake duration tb. The brake duration tb can be acquired from a time during which the brake pressure Pb is generated. The processor 101 acquires the sensor detection information 300 based on the result of detection by the sensor 50. The sensor detection information 300 is stored in the storage device 102.
Temperature history information 400 indicates the temperature history that is a history of the temperature applied to the brake pad 30. In particular, the temperature history information 400 indicates the temperature history of the contact surface 31 of the brake pad 30. The temperature history information 400 may further indicate a profile of the temperature history of the brake pad 30 in the depth direction d.
During the braking of the vehicle 1, the processor 101 generates and updates the temperature history information 400. A method of generating and updating the temperature history information 400 will be described later. The temperature history information 400 is stored in the storage device 102.
Wear volume function information 500 indicates the wear volume function f. The wear volume function f expresses the wear volume W as a function of the vehicle speed V, the brake pressure Pb, and the brake duration tb (see the above Equation (1)). The wear volume W increases as the vehicle speed V becomes higher. The wear volume W increases as the brake pressure Pb becomes higher. The wear volume W increases as the brake duration tb becomes longer.
Moreover, the wear volume W increases as the temperature applied to the contact surface 31 of the brake pad 30 in the past becomes higher. Therefore, according to the present embodiment, different wear volume functions f are prepared for each temperature history of the contact surface 31. That is, the wear volume function information 500 indicates the wear volume function f for each temperature history.
Each wear volume function f (f0 to f3) may be a formula or may be a map. Each wear volume function f is designed in advance based on actual measurements of the vehicle speed V, the brake pressure Pb, the brake duration tb, the temperature history of the contact surface 31, and the wear volume W. It should be noted that on designing the wear volume function f, a temperature of the contact surface 21 of the brake rotor 20 having a higher thermal conductivity is measured instead of the temperature of the contact surface 31 of the brake pad 30. Then, the measured temperature of the contact surface 21 of the brake rotor 20 is regarded as the temperature of the contact surface 31 of the brake pad 30.
The wear volume function information 500 thus generated is stored in advance in the storage device 102.
Estimated wear volume information 600 indicates the wear volume W that is estimated (calculated) by the wear volume estimation device 100 (i.e., the processor 101). The estimated wear volume information 600 may indicate the cumulative wear volume Wt which is an integrated value of the wear volume W. A method of estimating the wear volume W will be described later. The estimated wear volume information 600 is stored in the storage device 102.
During the braking of the vehicle 1, the information acquisition unit 110 acquires the sensor detection information 300 based on the result of detection by the sensor 50. The sensor detection information 300 includes the vehicle speed V, the brake pressure Pb, and the brake duration tb.
The temperature estimation unit 120 executes a “temperature estimation process” that estimates the temperature of the contact surface 31 of the brake pad 30. The temperature of the contact surface 31 increases as the frictional heat between the brake rotor 20 and the brake pad 30 increases. Therefore, the temperature of the contact surface 31 becomes higher as the vehicle speed V becomes higher. The temperature of the contact surface 31 becomes higher as the brake pressure Pb becomes higher. The temperature of the contact surface 31 becomes higher as the brake duration tb becomes longer. That is, the temperature of the contact surface 31 is expressed by the following Equation (2).
Te=g(V,Pb,tb) Equation (2):
In the Equation (2), Te is the estimated temperature of the contact surface 31. A temperature function g expresses the estimated temperature Te of the contact surface 31 as a function of the vehicle speed V, the brake pressure Pb, and the brake duration tb. The temperature function g may be a formula or may be a map. The temperature function g is designed in advance based on actual measurements or theories.
In the temperature estimation process, the temperature estimation unit 120 receives the sensor detection information 300 from the information acquisition unit 110. Then, the temperature estimation unit 120 calculates the estimated temperature Te of the contact surface 31 based on the sensor detection information 300 (V, Pb, tb) and the temperature function g.
A temperature of the brake rotor 20 may be estimated as the temperature of the contact surface 31 of the brake pad 30. For example, a temperature variation ΔT of the brake rotor 20 is expressed by the following Equation (3).
In the Equation (3), ΔTb is an amount of increase in temperature due to braking energy, ΔTc is an amount of decrease in temperature due to cooling, r is an effective braking radius, R is a tire radius, Ap is a piston area, μ(V) is a friction coefficient between the contact surfaces 21 and 31, As is a surface area of a sliding portion of the brake rotor 20, Ms is a weight of the sliding portion of the brake rotor 20, c is a specific heat of the brake rotor 20, h(V) is a thermal conductivity of the brake rotor 20, Tpre is a previous temperature of the brake rotor 20, and Tair is an air temperature.
The temperature estimation unit 120 calculates the temperature of the brake rotor 20 by calculating the temperature variation ΔT expressed by the Equation (3) at regular intervals (e.g., 0.1 sec). The temperature of the brake rotor 20 is used as the estimated temperature Te of the contact surface 31.
As described in the foregoing
The penetration depth estimation unit 130 executes a “penetration depth estimation process” that estimates the penetration depth Dp. The penetration depth Dp depends on the temperature Te of the contact surface 31 and the brake duration tb. The penetration depth Dp increases as the temperature Te of the contact surface 31 becomes higher. The penetration depth Dp increases as the brake duration tb becomes longer. That is, the penetration depth Dp is expressed by the following Equation (4).
Dp=h(Te,tb) Equation (4):
A penetration depth function h expresses the penetration depth Dp as a function of the estimated temperature Te of the contact surface 31 and the brake duration tb. The penetration depth function h may be a formula or may be a map. The penetration depth function h is designed in advance based on actual measurements or theories.
In the penetration depth estimation process, the penetration depth estimation unit 130 receives information on the estimated temperature Te and the brake duration tb from the temperature estimation unit 120. Then, the penetration depth estimation unit 130 calculates the penetration depth Dp based on the estimated temperature Te, the brake duration tb, and the penetration depth function h.
The temperature history management unit 140 manages the temperature history information 400 (see
It should be noted that the temperature history information 400 may indicate only the temperature history of the contact surface 31 and may not include the profile in the depth direction d. In that case, the temperature history management unit 140 updates the temperature history information 400 based on the estimated temperature Te of the contact surface 31.
The wear volume calculation unit 150 executes a “wear volume calculation process” that calculates the wear volume W caused by the brake operation this time. The wear volume calculation process is executed in parallel with the temperature estimation process and the penetration depth estimation process described above.
In the wear volume calculation process, the wear volume calculation unit 150 receives the temperature history information 400 from the temperature history management unit 140. The temperature history information 400 here is the one acquired at the time of the previous braking. The wear volume calculation unit 150 variably sets the wear volume function f according to the temperature history of the contact surface 31 indicated by the temperature history information 400.
More specifically, the wear volume function information 500 described above indicates the wear volume function f for each temperature history of the contact surface 31 (see
The selected wear volume function fs in the case of the wear volume function information 500 shown in
The selected wear volume function fs in the case of the wear volume function information 500 shown in
Then, the wear volume calculation unit 150 calculates the wear volume W by using the selected wear volume function fs. More specifically, the wear volume calculation unit 150 receives the sensor detection information 300 (V, Pb, tb) from the information acquisition unit 110. Then, the wear volume calculation unit 150 uses the selected wear volume function fs to calculate the wear volume W according to the vehicle speed V, the brake pressure Pb, and the brake duration tb.
The wear volume calculation unit 150 generates the estimated wear volume information 600 indicating the calculated wear volume W. The wear volume calculation unit 150 may calculate the cumulative wear volume Wt by integrating the wear volume W calculated for each brake operation. In this case, the estimated wear volume information 600 indicates the cumulative wear volume Wt as well.
If the cumulative wear volume Wt exceeds a threshold value, the wear volume calculation unit 150 may output an alert through the output device 60 (e.g., a display, a speaker).
Moreover, the wear volume calculation unit 150 provides the temperature history management unit 140 with the information of the calculated wear volume W. The temperature history management unit 140 moves the position of the contact surface 31 in the temperature history information 400 by a depth corresponding to the wear volume W caused this time. That is to say, the temperature history management unit 140 reflects the wear volume W caused this time in the profile of the temperature history of the brake pad 30 in the depth direction d. In other words, the temperature history management unit 140 updates the temperature history information 400 by updating the profile of the temperature history of the brake pad 30 in the depth direction d based on the wear volume W caused this time.
According to the present embodiment, as described above, the temperature of the contact surface 31 of the brake pad 30 that comes in contact with the brake rotor 20 is estimated during the braking of the vehicle 1. Then, the temperature history information 400 indicating the temperature history of the contact surface 31 is updated based on the temperature of the contact surface 31. When calculating the wear volume W of the brake pad 30, the temperature history of the contact surface 31 indicated by the temperature history information 400 is taken into consideration. More specifically, the wear volume function f used for calculating the wear volume W of the brake pad 30 is not fixed but variably set according to the temperature history of the contact surface 31. As a result, the estimation accuracy of the wear volume W is improved.
Moreover, according to the present embodiment, it is possible to estimate the wear volume W with high accuracy by utilizing the existing sensor 50 (i.e., the brake pressure sensor 51 and the wheel speed sensor 52). For example, the temperature of the contact surface 31 of the brake pad 30 is estimated based on the vehicle speed V, the brake pressure Pb, and the brake duration tb. A temperature sensor dedicated to the temperature estimation process is unnecessary. This is useful from a viewpoint of cost reduction.
Furthermore, according to the present embodiment, the cumulative wear volume Wt of the brake pad 30 is automatically calculated. Thus, a failure of the brake pad 30 can be detected automatically regardless of the driver. The present embodiment may be applied to a case where no fixed driver exists (e.g., automated driving vehicle, car sharing).
| Number | Date | Country | Kind |
|---|---|---|---|
| 2020-128562 | Jul 2020 | JP | national |
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| 4790606 | Reinecke | Dec 1988 | A |
| 5651431 | Kyrtsos | Jul 1997 | A |
| 20080236269 | Howell et al. | Oct 2008 | A1 |
| 20180208300 | Bill | Jul 2018 | A1 |
| 20220018413 | Matsui | Jan 2022 | A1 |
| 20230226859 | Bill | Jul 2023 | A1 |
| Number | Date | Country |
|---|---|---|
| 101349313 | Jan 2009 | CN |
| 2015-121251 | Jul 2015 | JP |
| 6207075 | Oct 2017 | JP |
| WO-2018099864 | Jun 2018 | WO |
| Number | Date | Country | |
|---|---|---|---|
| 20220034379 A1 | Feb 2022 | US |
