Method and system for analyzing the wear behavior of brake pads/linings

Abstract

A method for analyzing the wear behavior of brake pads of a brake system has at least the following steps: a) providing a brake system with at least one or more brakes, each with one or more brake pads which each have a pad carrier plate and a friction lining composed of at least two or more friction material layers which are composed of different friction materials; and at least one evaluation device; b) determining the wear which is brought about per brake during braking operations with at least one wear sensor per brake; c) determining the braking energy which is brought about per brake during braking operations with the evaluation device; d) repeated determination of an instantaneous gradient of a curve which relates the values determined in steps b) and c) and preferably a route information item to one another; and e) outputting a signal at an output device if the gradient changes.

Claims

1. A method for analyzing wear behavior of brake pads, the method comprising the steps of: a) providing a brake system comprising an evaluation device and at least one or more brakes, each brake including one or more brake pads which have a pad carrier plate and a friction lining composed of two or more layers of friction material having different coefficients of friction; b) determining wear per brake which occurs during braking by way of at least one wear sensor per brake; c) determining braking energy per brake during braking by way of the evaluation device; d) repeatedly determining a momentary increase in a curve correlating values determined in steps b) and c) to each other; and e) emitting a signal to an output device when the momentary increase changes.

2. The method as claimed in claim 1, wherein a signal is emitted at the output device in step e) at least when a slope exceeds a prescribed limiting value.

3. The method as claimed in claim 1, wherein a signal is emitted by an output device in step e) at least when a slope exceeds a tolerance range or a tolerance band.

4. The method as claimed in claim 1, wherein all of the brake pads of the brake system have a lining carrier plate and a friction lining composed of two or more layers.

5. The method as claimed in claim 1, wherein a thickness of at least one of the layers of friction material in the at least one brake pad corresponds to a final wear level of said brake pad, and wherein a signal is emitted when said final wear level is detected.

6. The method as claimed in claim 1, wherein step d) further correlate route information.

7. A brake system, comprising: at least one or more brakes, each brake including one or more brake pads which have a pad carrier plate and a friction lining composed of two or more layers of friction material having different coefficients of friction and composed of different friction materials; and at least one evaluation device, the evaluation device being configured to execute a process to: a) determine wear per brake which occurs during braking by way of at least one wear sensor per brake; b) determine braking energy per brake during braking by way of the evaluation device; c) repeatedly determine a momentary increase in a curve correlating values determined in steps b) and c) to each other; and d) emit a signal to an output device when the momentary increase changes.

8. The brake system as claimed in claim 7, wherein a thickness of at least one of the layers of friction material in the at least one brake pad corresponds to a final wear level of said brake pad.

9. The brake system as claimed in claim 8, wherein the thickness of one of the outer layers of friction material is greater than the thickness of the inner layer of friction material.

10. The brake system as claimed in claim 9, wherein the brakes are disc brakes.

11. The brake system as claimed in claim 10, wherein the disc brakes are configured as pneumatic disc brakes.

12. The brake system as claimed in claim 7, wherein step c) further correlates route information.

13. A brake pad for use in a brake system comprising at least one or more brakes, and at least one evaluation device configured to execute a process to: a) determine wear per brake which occurs during braking by way of at least one wear sensor per brake; b) determine braking energy per brake during braking; c) repeatedly determine a momentary increase in a curve correlating values determined in steps b) and c) to each other; and d) emit a signal to an output device when the momentary increase changes, comprising: a pad carrier plate and a friction lining composed of at least two or more layers of friction material with different coefficients of friction, wherein a thickness of one of the friction material layers corresponds to a final wear level of the brake pad.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1A is a highly schematic and simplified representation of a known vehicle brake system.

(2) FIG. 1B is a highly schematic and simplified representation of a vehicle brake system according to an embodiment of the invention.

(3) FIG. 2 is a top view of a brake pad for a vehicle.

(4) FIGS. 3-8 are diagrams indicating the wear of a lining material as a % of the lining material as a function of the vehicle mileage.

DETAILED DESCRIPTION OF THE DRAWINGS

(5) FIG. 1B shows a vehicle brake system comprising four disc brakes 1, 2, 3, 4, which are disposed on two axles 5a, b and which have two brake pads 6a, 6b each. During braking, each of the brake pads is pressed frictionally against a brake disc, which is not shown here. As in the prior art shown in FIG. 1A, it is provided that each of the four disc brakes 1-4 has a wear sensor 7, the outputs of which are each connected 8 to the evaluation device 9 so that, when the vehicle is in operation, information about the respective wear state of the disc brakes 1 through 4 is available on the evaluation device. According to one variant of the invention, it may be possible to omit terminals for the wear sensors, which leads to a reduction in costs, although alternatively it is also possible to keep them.

(6) According to the invention, the current total wear of both brake pads and the brake disc is still recorded by a wear sensor 7, especially as described above. This value is not considered in isolation, though. Rather, an energy analysis is also performed. Thus, for example, signals regarding the rotation angle of the vehicle wheels (rotation angle sensor 14 on the wheels and/or near the disc brakes 1-4) and preferably regarding the torque (pressure sensor 16) as well as preferably information about the overall performance of the vehicle (preferably since a pad replacement, if one has already been carried out) are provided and evaluated in the evaluation device 9.

(7) The braking energy can be detected in various ways here, such as in the manner according to DE 101 50 047 A1 or DE 199 33 961 A1 as described above. The converted braking energy substantially corresponds to the energy input during braking operations.

(8) FIG. 2 shows an advantageous brake pad 6a and b for a brake system of a vehicle having at least one or more disc brakes 1 through 4. This brake pad is advantageously suitable for the method according to the invention. The brake pad 6a is shown in a state in which wear has not yet occurred.

(9) The brake pad 6a has a pad carrier plate 10, on which a friction lining 11 is disposed. The friction lining 11 consists of at least two layers of friction material 12, 13, which have different coefficients of friction and can be composed, for example, entirely or partially of different materials. The first layer of friction material 12 is arranged directly on the pad carrier plate 10. The second layer of friction material 13 is arranged on the side of said pad carrier plate 10 which faces away from the carrier plate 1.

(10) Preferably, the thickness D1 of the first layer of friction material 12 between the pad carrier plate 10 and the second layer of friction material 13 is less than the thickness D2 of the second (outer) layer of friction material 13. The thickness D1 of the inner layer of friction material 12 preferably corresponds to a final wear level. This is a level at which a residual layer of lining material is still present on the carrier plate 10, but at which a pad replacement must be carried out immediately or at least within a prescribed remaining mileage interval in order to avoid a state in which the safety of the operation is jeopardized.

(11) For this reason, the thickness D2 of the outer layer of friction material 13 is preferably dimensioned such that the outer layer of friction material 13 has been completely worn away once the final wear level is reached. Reaching this state is thus a suitable indicator to the driver that it will soon be necessary to replace the pads. Therefore, it is advantageous to detect in a simple way when this state is reached, and in particular to detect it in each brake pad of a vehicle individually.

(12) Modern information systems in the vehiclesee the previously mentioned document DE 101 50 047 A1process a multitude of data and measurement variables that, on the one hand, can be used to provide the driver and/or the vehicle operator information e.g for the planning of service intervals and, on the other hand, are also beneficial in simplifying diagnoses in service workshops in the event of malfunctions. An evaluation of wear is thereby possible. If this evaluation of wear is correlated with the energy converted during braking, the information about the distance already driven can also be used to determine the specific wear of the brake pads 6a, b of the disc brakes 1-4, based on the mileage in the form of a slope gradient, and can be stored in the memory.

(13) Using this information, for instance, it is also possible to make a prediction about the remaining useful life of the brake pads. After a defined driving distance or service life of the vehicle, a comparison is carried out between the saved slope gradient and the new current gradient. If a significant change is detected, then the vehicle electronics can initiate an appropriate, freely definable action, e.g. emitting a warning signal for the driver.

(14) In order to recognize when the brake pads reach the final wear level using the method described, brake pads 6a, b are installed that have a friction lining 11 supplied e.g. according to FIG. 2. The outer layer of friction material 13 appropriately has thickness D2, and the final wear level is reached at this amount of wear. If required, the brake pad 6a, b can also comprise more than two layers of friction material 12, 13 (not shown), wherein these layers of friction material 12, 13 can consist of two different material compositions, which are then alternatingly compressed, for example, or can also consist of multiple different materials so that the progression of the wear can be resolved in even greater detail, which could improve e.g. the quality of a possible prediction of the useful life of the brake pads. It should be noted that brake pads constructed from multiple layers of friction materials 12, 13 are known per se from the prior art. However, the essential advantages of said linings in connection with the monitoring of wear were not recognized.

(15) If, with the aid of wear sensors 7 on the brakes, the wear evaluation is correlated with the energy converted during braking, influences such as a changing driving behavior and the like are not taken into account for the most part. Using the information about the distance already driven, a specific amount of wear can be calculated in the form of a slope gradient with respect to the service life of the brake pads.

(16) As is shown in FIG. 3 through 8, at least one curve per wheel, in particular a straight line in at least some sections, is formed for each wheel and/or disc brake, and the slope or gradient of the curve is specific to the respective friction material. Thus if the slope changes, it may indicate, for example a change in the friction material or coefficients of friction.

(17) A signal is preferably emitted to an output device at least when the slope changes beyond at least one predetermined fixed or variable limiting value. It is ensured in this way that the changes that arise are also significant enough that it is necessary to emit a signal. It is especially preferred that this be accomplished in that a signal is emitted by an output device in step f) at least when the slope exceeds a tolerance range or a tolerance band TB-VA or TB-HA. The tolerance range can be constant or can change, e.g. increase linearly, with increasing mileage.

(18) When the transition from one friction material layer 13, 12 to the other is crossed, the brake system detects a change by way of step d) and/or by comparing the wear gradients. Preferably, a defined action is then triggered.

(19) In the case of a double-layered friction material with layers of friction material 12, 13, wherein the thickness D1 of the friction material layers 12 lying directly against the pad carrier plate correspond approximately to the final wear level, the transition between the two materials can be detected by the change in gradient and can be displayed to the driver, such as on a screen or the like. (FIGS. 3-8). This replaces the function of a known cable wear sensor (terminal sensor).

(20) FIG. 3 shows a diagram in which a degree of wear in % relative to the mileage is applied as route information (since the last pad replacement).

(21) The wear in % is thus a value that is determined e.g. from the quotient of a measured wear value and the calculation of the energy input during braking operations. This value is summed and plotted relative to the mileage. The resulting curve shows that after (or on) reaching a particular mileage (ca. 300,000 km) in all four disc brakes 1-4 of the two axles 5a, b of a vehicle brake system, the wear gradient changes, which indicates that the ratio between the measured wear value and the value from the calculation of energy input has changed. This demonstrates a transition from the outer layer of friction material 13 to the inner layer of friction material 12. The final wear level has been reached. A warning is emitted (immediately or at least within a prescribed mileage interval).

(22) Also marked in FIG. 3 are a tolerance band TB-VA for the front axle and a tolerance band TB-HA for the rear axle. Only when the curves lead out of the associated tolerance band TB-VA or TB-HA is it necessary to display a warning signal (in this case at ca. 300,000 km). Corresponding tolerance bands TB-VA and TB-HA are also shown in FIGS. 5, 6, 7 and 8. Here, the span of tolerance bands TB-VA and TB-HA increases as the mileage increases (measured from the last pad replacement), which is preferred but is not obligatory.

(23) FIG. 4 shows that the wear gradient changes after (or on) reaching a particular mileage (ca. 300,000 km) only at the two disc brakes 1-2 of the front axle of a vehicle brake system. This demonstrates a transition at this axle from the outer layer of friction material 13 to the inner layer of friction material 12. In this instance, the final wear level on the front axle 5a is reached before the corresponding level is reached on the rear axle 5b. A warning is emitted (immediately or at any rate within a prescribed mileage interval) after one or both tolerance bands TB-HA and/or TB-VA is/are reached.

(24) FIGS. 5 and 6 show that the wear gradient changes after (or on) reaching a particular mileage (ca. 300,000 km) on only one of the two disc brakes 2 of the front axle of a vehicle brake system, wherein the change is more pronounced in FIG. 5 than in FIG. 6.

(25) It is apparent from each of FIGS. 5 and 6 that a transition from the outer layer of friction material 13 to the inner layer of friction material 12 has taken place only at one of the disc brakesdisc brake 2of this axle 5athe front axle in this case. The final wear level has therefore already been reached on the disc brake 2 of the front axle 5a. Thus a warning is also emitted here (immediately or at any rate within a prescribed mileage interval). This is because a change in the wear gradient also occurs when only one of the brake pads in the disc brake has reached its final wear level. FIG. 5 shows how this can be the case if one side is heavily soiled or e.g. if a malfunction, such as a defective caliper guide, occurs in the disc brake. These can prevent a pad from being completely worn out and, in the most unfavorable case, from being pulled through between the brake disc and carrier. The known total wear detection method usually cannot detect this malfunction.

(26) FIG. 7 and FIG. 8 show representations similar to those in FIGS. 3 and 4, but in which a degree of wear is applied via the energy input. This results in a constant and/or a straight line with a gradient of zero. Once again, as is shown in FIGS. 3 and 4, any deviation from this gradient of zero leads out of a tolerance band TB-HA and/or TB-VA and results in a warning signal.

LIST OF REFERENCE SIGNS

(27) 1 Disc brake 2 Disc brake 3 Disc brake 4 Disc brake 5a, b Axles 6a, b Brake pad/lining 7 Wear sensors 8 Cable 9 Evaluation device 10 Pad carrier plate 11 Friction lining 12, 13 Layers of friction material 14 Pole wheel sensor 15 Pressure sensor

(28) The foregoing disclosure has been set forth merely to illustrate the invention and is not intended to be limiting. Since modifications of the disclosed embodiments incorporating the spirit and substance of the invention may occur to persons skilled in the art, the invention should be construed to include everything within the scope of the appended claims and equivalents thereof.