Brake for motor vehicle

Abstract

A brake for a motor vehicle and a method for determining the braking torque of a disc brake are proposed. This makes use of the fact that the brake lining is electrically conductive and thus an electric current can be generated between the brake disc and the brake lining by applying a test voltage of locally varying current strength. The current strength depends on whether the brake disc and the brake lining are in contact with each other in the relevant region and how great the contact pressure acting on the relevant region is. The current can be read by means of a circuit with parallel shunt resistors.

Description

Technical Field

[0001] This invention relates to a brake having a brake disc and brake pads, a braking system, a method for determining the braking torque of the brake, and a motor vehicle. Background Technology

[0002] In motor vehicles equipped with brakes, it is typically necessary to determine the current braking torque. Especially in autonomous or semi-autonomous vehicles, it is also necessary to be able to set a desired braking torque, for example, to achieve a desired deceleration. A commonly available parameter is the braking pressure, which can be easily set. Theoretically, the braking torque can be approximated based on this braking pressure, a previously determined coefficient of friction between the brake pads and brake disc, wheel speed, and the geometry of the wheel brakes. Furthermore, the braking torque can be approximated based on changes in the vehicle's kinetic and potential energy, air resistance, and rolling resistance. A drawback of the latter calculation method is that, due to existing load conditions and mass distribution, only sophisticated sensors can be used to determine the vehicle's total mass with sufficient accuracy. However, with the calculation method mentioned first, it is unknown which surfaces between the brake disc and brake pads are engaged during braking. Therefore, the effective friction radius, the pad friction coefficient, and the variables mathematically derived from this (e.g., braking torque and braking work) can only be determined imprecisely.

[0003] To improve the determination of the mating surface (or pressure distribution) and the derivation of related, more accurate subsequent variables such as effective friction radius and braking torque, various methods, such as pressure foil-based, fiber Brake grating (FBG)-based, brake pad-based pressure sensor-based, or GOM-based measurements, were tested. Previous methods have drawbacks because they are sometimes only applicable statically and / or complex and costly to use. Furthermore, the methods mentioned are generally not suitable for unrestricted use in practice due to their limited measurement range (e.g., in terms of operating temperature range), sensor drift, or significant impact on the structural integrity of the brake pads. To date, none of the methods mentioned have proven suitable for use in vehicles, such as during testing, including test drives of development vehicles.

[0004] A system for indicating wear on brake pads is known from US 2016 / 0305502 A1. This system includes a brake housing, brake pads mechanically connected to the brake housing, and a sensor mechanically connected to the brake pads. The sensor can determine when the brake pads have been worn to a predetermined position by a rotating part of the wheel (e.g., a brake disc). The system may also include an electronic module electrically connected to the sensor and mechanically connected to the brake housing. The electronic module may include a radio frequency antenna configured to wirelessly receive radio frequency energy from an external radio frequency transmitter and an energy converter electrically connected to the radio frequency antenna. The electronic module may include an internal transmitter electrically connected to the energy converter and the radio frequency antenna. While the described system can detect wear on brake pads, it does not provide a more precise method for determining braking torque, coefficient of friction, or similar data. Summary of the Invention

[0005] Therefore, the objective of this invention is to provide a method for determining the braking torque in a disc brake of a motor vehicle as accurately as possible.

[0006] According to the present invention, this task is achieved by a brake for a motor vehicle having a brake disc and brake pads, the brake being configured to apply a voltage between the brake disc and brake pads, and the brake pads having a plurality of electrical contact points capable of spatially resolving the current flowing between the brake disc and brake pads. This task is also solved by a braking system having such a brake and evaluation electronics for spatially resolving the current flowing between the brake disc and brake pads, the task being solved by a method for determining the braking torque of a brake having a brake disc and brake pads, comprising the following steps:

[0007] a. Apply voltage between the brake disc and the brake pads.

[0008] b. Identify multiple currents flowing between the brake disc and brake pads, each current being assigned to the electrical contact points of the brake pads.

[0009] c. Determine the effective friction radius of the brake using a given current.

[0010] d. Determine the braking pressure of the brake.

[0011] e. Determine the current coefficient of friction between the brake pads and the brake disc, or

[0012] f. Determine the braking torque based on the determined current braking pressure, the friction characteristic map of the brake stored in the memory, and the determined current effective friction radius.

[0013] This task can also be solved by motor vehicles that have such brakes or such braking systems.

[0014] According to the present invention, it has been recognized that the fact that ordinary brake pads have a high metal content of up to 65% can be utilized, meaning they can be used as electrical conductors. By spatially resolving the measurement of the current flowing from the brake disc through the brake pads, information about the contact area between the brake disc and the brake pads can be obtained. In other words, it can be determined which area(s) of the brake pads are currently in contact with the brake disc. For example, conclusions about the current braking torque can be drawn. The electrical contact point can also be referred to as the measurement point.

[0015] In other words, it utilizes the fact that brake pads are conductive, so a current flowing between the brake disc and brake pads can be generated by applying a test voltage. The intensity of this current varies locally. The current intensity depends on whether the brake disc and brake pads are in contact with each other in the relevant area, and the magnitude of the contact pressure acting on that area. The current can be read using a circuit with a shunt resistor in parallel.

[0016] It can be specified that the current flowing out of the brake pads can be measured at multiple different measuring points on the brake pads. Then, multiple portions of the current can flow from the brake disc through the brake pads along different current paths to the corresponding measuring points. If a closed circuit exists, the current flowing through the corresponding current path can be measured. This is the case during braking because the brake disc is in contact with the brake pads.

[0017] Current flows along the path of lowest resistance. Therefore, more current flows through the path to the first measuring point, closer to the contact area of ​​the brake disc and brake pads, compared to the current path through the second measuring point, which is farther from the contact area between the brake disc and brake pads. In other words, the current flows more strongly through the nearest current path. At the mating surface where the brake pads contact the brake disc, the higher current then flows from the brake disc into the brake pads and to the corresponding measuring point. Based on the number of measuring points and their distribution within the brake pads, detailed information about the contact or mating area between the brake disc and brake pads can be obtained.

[0018] Furthermore, the resistance of brake pads varies planarly and locally depending on the pressure acting on them. Therefore, brake pads can be used as pressure sensors and also to determine data such as current braking torque.

[0019] Using this structure, the engagement surface between the brake disc and brake pads can be dynamically determined. This allows for precise determination of the coefficient of friction and braking torque between the brake disc and brake pads. The brake pads themselves are used as part of the sensing structure. The brake pads act as planar pressure sensors. Therefore, expensive additional devices are not required to determine the coefficient of friction and / or braking torque. The necessary components can be integrated extremely cost-effectively. Furthermore, due to their small size, the solution according to the invention is substantially suitable for vehicle use, such as during test drives.

[0020] This invention enables targeted optimization of braking systems, thus offering the potential for cost reduction and efficiency improvement. The coordination of the software used can be improved. For example, a brake temperature model can be created and then used to control the fan or cool the brakes. This solution is suitable for use in test benches and vehicles, for example, as part of testing. Only minimal intervention is required in the structure of the brake under inspection, resulting in realistic results that can be easily used in practice. For example, a friction coefficient estimator, a brake wear indicator, or a mass estimator for estimating vehicle mass can also be created.

[0021] According to an advantageous embodiment, the brake has a sliding contact connected to a voltage source to apply voltage between the brake disc and the brake pads. In this way, a robust and easily constructed option can be created to apply the required tension between the brake disc and the brake pads. This sliding contact can also be easily modified.

[0022] Advantageously, the electrical contact points can be designed as multiple connection points for wires arranged on the side of the brake pad opposite to the friction surface of the brake pad. The wires can then be led out of the brake pad on the side away from the friction surface.

[0023] The electrical contact point can be arranged within the volume of the brake pad. In other words, the current is then absorbed by current-dissipating wires within the volume of the brake pad. The contact surface is not located on the surface of the brake pad, but at a certain distance from it. Placing the measuring point near the friction surface within the brake pad material improves measurement accuracy. However, placing the measuring point further away from the friction surface creates a more robust system that can still function even if the brake pad is partially worn. Favorable locations for the measuring point along the thickness of the brake pad (in other words, in the axial direction of the brake disc) can be 10% to 90%, 20% to 80%, or 30% to 70% of the brake pad thickness on the side of the brake pad facing the brake disc.

[0024] In an alternative embodiment, the measuring points are arranged on the surface of the brake pad opposite the brake disc or opposite the friction surface. This design is particularly robust and simple in structure.

[0025] Electrical contacts can be formed by electrical conductors arranged in blind holes that open toward the side of the brake lining opposite the brake disc. The blind holes can extend perpendicularly to the brake lining surface facing the brake disc. Furthermore, the blind holes or electrical contacts can be uniformly distributed on the brake lining. The electrical contacts can be arranged, for example, along a grid or mesh. The electrical contacts can also be arranged at different distances from the lining friction surface inside the lining and / or from the brake lining surface facing the brake disc. In other words, the electrical contacts can be arranged at different depths within the brake lining. The grid or mesh can be a three-dimensional grid or mesh.

[0026] Electrical contacts can come into contact with cables. For example, a thin cable can protrude from the back of the brake pad (in other words, from the side of the brake pad opposite the friction surface) into the brake pad to a certain depth. This depth can be, for example, between 10% and 90% of the brake pad thickness, between 20% and 50% of the brake pad thickness, or between 30% and 40% of the brake pad thickness.

[0027] Advantageously, the brake pad has a first brake pad portion disposed on a first side of the brake disc and a second brake pad portion disposed on a second side of the brake disc opposite to the first side of the brake disc. Both the first and second brake pad portions have multiple electrical contact points capable of spatially resolving the measurement of the current flowing between the brake disc and the brake pad. In other words, a portion of the brake pad can be disposed on both sides of the brake disc, in which case the two portions of the brake pad are designed to spatially resolve the current flowing through the brake pad. Both portions of the brake pad can have the configuration described previously.

[0028] According to an advantageous embodiment, the brake according to the invention works in conjunction with evaluation electronics for determining, in a spatially resolved manner, the current flowing between the brake disc and the brake pads. The evaluation electronics may have a plurality of shunt resistors connected in parallel with each other. Each shunt resistor may be associated with one of the electrical contact points of the brake pads. The voltage present therein can then be determined by the corresponding shunt resistor. In this way, the current flowing through the associated electrical contact point or measurement point can then be determined. The shunt resistors may, for example, have a resistance value between approximately 50 ohms and approximately 10 megohms.

[0029] The evaluation electronics can work in conjunction with or be part of a control unit that is configured to calculate the current braking torque, and the spatial resolution of the current is determined by taking into account the current flowing between the brake disc and brake pads when calculating the current braking torque.

[0030] The method according to the present invention is characterized by the following steps

[0031] a. Apply voltage between the brake disc and the brake pads.

[0032] b. Identify multiple currents flowing between the brake disc and brake pads, each current associated with an electrical contact point of the brake pads.

[0033] c. Determine the effective friction radius of the brake using a given current.

[0034] d. Determine the braking pressure of the brake.

[0035] e. Determine the current coefficient of friction between the brake pads and the brake disc, or

[0036] f. Determine the braking torque based on the determined current braking pressure, the friction characteristic map of the brake stored in the memory, and the determined current effective friction radius.

[0037] This process can be run continuously in real time. Alternatively, data on the determined current can be recorded and subsequently evaluated. This method is particularly advantageous when testing newly designed brakes or new motor vehicles, as it allows for precise characterization of the brake's functionality.

[0038] Here, steps e. and f. are performed alternately. Different usage scenarios must be distinguished: the coefficient of friction of the brake can be determined, for example, on a test bench, or the braking torque itself can be determined, for example, during use in a vehicle. Therefore, the method according to the invention is used either to determine the coefficient of friction (test bench) or to determine the braking torque (vehicle).

[0039] Process steps a through d must be performed regardless. The current coefficient of friction can then be determined via method step e. Alternatively, the braking torque can be calculated by performing method step f. For this purpose, an existing friction characteristic diagram is used; in other words, a diagram or table of known friction coefficients describing various parameters is used. The friction characteristic diagram can be stored in memory. The friction characteristic diagram can also be predetermined, for example, using the method according to the invention. In this case, for example, the method according to the invention can be performed on a test bench at the same location as method step e.

[0040] The method according to the invention can be performed, for example, using a brake or braking system according to the invention. For this purpose, a control device can be used, which may be, for example, an onboard computer or another computing unit present in the motor vehicle. The control device can be configured to calculate the relationship between braking pressure and braking torque based on a previously determined braking torque, so that the desired braking torque can be precisely set based on the braking pressure. Alternatively, the recorded data can be transmitted to an external computing unit for evaluation. This may occur during or after driving.

[0041] In the context of this specification, the effective friction radius is specifically understood as the effective radius of the assumed circumferential force acting tangentially on the brake disc during braking. The effective friction radius is calculated based on the distance from the central axis of the brake cylinder (or one of the brake cylinders, or if there are multiple brake cylinders) to the axis of rotation of the brake disc. Multiplying the circumferential force by the effective friction radius yields the braking torque. During braking, a circumferential force is generated when the brake pads are pressed against the brake discs on both sides due to the pressure from the brake cylinders. This force counteracts the rotational motion of the wheel due to the friction between the brake pads and the brake discs, as well as the clamping force. Attached Figure Description

[0042] Exemplary embodiments of the invention will be explained in more detail with reference to the accompanying drawings and the following description. The drawings show:

[0043] Figure 1 : A schematic diagram of a brake pad used in a brake according to the present invention.

[0044] Figure 2 The present invention provides a schematic diagram of the brake and a simplified equivalent circuit diagram of the evaluation electronics.

[0045] Figure 3 Schematic diagram of the electronic unit and equivalent circuit diagram of the brake pads.

[0046] Figure 4 A schematic diagram of the brake, used to illustrate the calculation of relevant variables.

[0047] Figure 5 The effective friction radius r is determined based on existing technology and the method according to the present invention. eff Comparison between them, and

[0048] Figure 6 : A diagram used to explain the calibration process. Detailed Implementation

[0049] Figure 1 A schematic diagram of a brake pad 6 used in a brake according to the invention is shown. The back surface of the brake pad 6 can be seen; in other words, the side of the brake pad 6 opposite the friction surface. It can be seen that a plurality of contact points 8 are distributed on the back surface of the brake pad 6, through which the brake pad 6 can be contacted to absorb current. The contact points 8 can be formed by holes or blind holes extending perpendicular to the surface of the brake pad 6. Parallel to the surface of the brake pad 6, there is a milled portion 12 starting from the contact points 8, from which a cable can be accommodated, the cable having electrical contact points 8 on one side and evaluation electronics, such as in the form of a circuit board, on the other side. The milled portion 12 prevents the cable from being squeezed by the brake pad of the brake during braking.

[0050] Figure 2 A schematic diagram of the brake 2 according to the invention and a simplified equivalent circuit diagram for evaluating the electronic equipment are shown. The mechanical components shown consist of a brake disc 4 and brake pads 6.1 and 6.2 arranged on both sides of the brake disc 4. Both brake pads 6.1 and 6.2 have contact points 8 into which cables 10 are inserted to contact electrical contact points on the bottom or end walls of the associated blind holes and to absorb and dissipate current emanating from them. Shunt resistors 16 are connected to cables 10. The voltage drop across these shunt resistors 16 can be measured using the measuring device 18 schematically shown.

[0051] Brake disc 4 is electrically contacted via sliding contact 14, also schematically shown, allowing voltage generated by voltage source 24 to be applied to brake disc 4. If brake disc 4 contacts brake pads 6.1 and 6.2 during braking, the circuit is closed and current flows from brake disc 4 through different regions of brake pads 6.1 and 6.2 and through shunt resistor 16. Based on the voltage drop across shunt resistor 16, the current flowing at the corresponding contact point 8 can be determined. Therefore, conclusions can be drawn regarding the type of contact between brake disc 4 and brake pads 6.1 and 6.2 in the regions of the corresponding contact points 8. The following formula can be used:

[0052] (1)U shunt,n = U in *R shunt,n / (R belag +R shunt,n )

[0053] (2)I shunt,n = U shunt,n / R shunt,n

[0054] U in To apply voltage to brake disc 4, U shunt,n Let I be the voltage drop across the nth shunt resistor. shunt,n R is the current flowing through the nth shunt resistor. shunt,n R is the resistance of the nth shunt resistor. belag The resistance of brake pad 6 associated with the nth contact point.

[0055] Figure 3 A schematic diagram of the electronic unit 20 and an equivalent circuit diagram of the brake pad 6 are shown. As already explained, the voltage U is generated through the contact between the brake pad 6 and the brake disc (not shown). in The voltage U is applied to the brake pad 6. in This results in current flowing through the resistor 34 and shunt resistor 16 (R_shunt) of the brake pad 6. The microcontroller 22 measures and processes the voltage U across the shunt resistor 16. shunt,nThe analog-to-digital converter (ADC) of the microcontroller 22 can be used for this task. The microcontroller 22 can be connected to the recorder 30 via a connector 28, in other words, to the storage unit, or to another control device 32, which can be, for example, a USB connector or another interface.

[0056] The evaluation electronics include an electronics unit 20 having a circuit board 26, which may be designed as a printed circuit board (PCB). Circuit board 26 has voltage dividers arranged in parallel and a slot for a commercially available microcontroller 26. The voltage dividers are measured and digitized using the ADC (analog-to-digital converter) input of the microcontroller 26. In this way, many voltage signals can be locally bundled on the brake and converted into suitable output signals, for example, into signals for a controller area network (CAN). The output signals generated in this way are then recorded by a recorder 30 or other suitable measurement technology located in the vehicle. For example, in a subsequent evaluation, the effective friction radius can be dynamically formed based on the center of gravity of the mating surfaces, and the braking power can be calculated using the current braking pressure, which can also be transmitted via, for example, CAN or a CAN bus.

[0057] Figure 4 A schematic diagram of brake 2 is shown to illustrate the calculation of relevant variables. Not only is the brake disc 4 shown, but also the brake pads 6. Furthermore, the effective friction radius r... eff Piston force FK and circumferential force FU are shown as relevant variables.

[0058] The following variables and equations can be used to calculate the friction coefficient and braking pressure:

[0059]

[0060] The following table summarizes the various application areas of the method according to the present invention and its differences from the prior art:

[0061]

[0062] Figure 5 The left side shows the determination of the effective friction radius r according to existing technology. eff The effective friction radius r is determined according to the method of the present invention on the right. effA comparison is shown. The brake disc 4 and brake cylinder 6 are schematically illustrated. On the right, instead of showing the brake cylinder 6 itself, a representation of the measured value 36 determined using the method according to the invention is shown, describing the position-dependent flowing current. These currents are the currents flowing through the shunt resistors. Therefore, they can also be referred to as shunt currents. According to the method of the invention, the area or pressure center can be determined based on the distribution of the shunt current. Therefore, the pressure acting on the brake cylinder can be determined in a spatially resolved manner based on the measured current. The distance from the surface or pressure center to the axis of rotation 38 of the brake disc 4 can then be used as the dynamic effective friction radius r. eff,dyn .

[0063] The shunt resistors assigned to specific measurement points on the brake pads can be adapted in terms of size or resistance value to the corresponding pad resistance value for that measurement point. These values ​​may differ for different measurement points due to the inhomogeneity of the brake pad material. Therefore, shunt resistors can be used to calibrate the system. To do this, the pad resistance value for each measurement point is determined after the cable is inserted. The shunt resistors are then sized to obtain approximately equal voltage divider voltages.

[0064] The following is for reference. Figure 6 The calibration process is explained in more detail. Brake pad 6 is shown with measurement points 40.1, 40.2, 40.3, and 40.4. Furthermore, a cross-section through brake pad 6 is schematically shown, with cable 10 inserted at contact point 8. The resistance R between cable 10 and the side of brake pad 6 opposite to cable 10 is then measured in the region of contact point 8. The measurement point may be wetted to improve local conductivity. For clarity, contact points A and B are schematically shown here, and are also used in the schematic representation of measuring device 42 to indicate the measurement path. Based on the resistance measured for each measurement point 40.1, 40.2, 40.3, and 40.4, the size of the shunt resistor can then be selected such that the current flowing through the measurement path is theoretically or mathematically approximately the same.

[0065] List of reference numerals

[0066] 2. Brake

[0067] 4. Brake disc

[0068] 6 Brake pads

[0069] 8 Contact points

[0070] 10 Cables

[0071] 12 Milling section

[0072] 14 Sliding Contact

[0073] 16 Shunt Resistor

[0074] 18 Measuring devices

[0075] 20 electronic units

[0076] 22 microcontrollers

[0077] 24 Voltage Source

[0078] 26 Circuit Boards

[0079] 28 connectors

[0080] 30 recorders

[0081] 32 Control device

[0082] 34 Partial Resistors

[0083] 36 Measured values

[0084] 38 Rotation axis

[0085] 40 measurement points

[0086] 42 Measuring device

[0087] A contact point

[0088] B contact point

Claims

1. A brake (2) for a motor vehicle, said brake having a brake disc (4) and brake pads (6), wherein, The brake (2) is configured to apply voltage between the brake disc (4) and the brake pad (6), wherein the brake pad (6) has a plurality of electrical contact points (8) that enable the determination of the position of the current flowing between the brake disc (4) and the brake pad (6).

2. The brake (2) according to claim 1, wherein, The brake (2) has a sliding contact (14) connected to a voltage source (24) for applying voltage between the brake disc (4) and the brake pad (6).

3. The brake (2) according to any one of the preceding claims, wherein, The electrical contact point (8) is designed as a plurality of connection points for wires, the plurality of connection points being arranged on the side of the brake pad (6) opposite to the friction surface of the brake pad (6).

4. The brake (2) according to any one of the preceding claims, wherein, The electrical contact point (8) is arranged within the volume of the brake pad (6).

5. The brake (2) according to any one of the preceding claims, wherein the electrical contact point (8) is formed by an electrical conductor arranged in a blind hole that opens toward the side of the brake pad (6) opposite to the brake disc (4).

6. A braking system having a brake (2) according to any one of the preceding claims, and having an evaluation electronic device for determining, in a spatially resolved manner, the current flowing between the brake disc (4) and the brake pads (6).

7. The braking system according to claim 6, wherein, The evaluation electronic device has a plurality of shunt resistors (16) connected in parallel with each other, and each of the shunt resistors (16) is associated with an electrical contact point (8) of the brake pad (6).

8. The braking system according to any one of claims 6 to 7, wherein, The evaluation electronics works in conjunction with or is part of the control device (32), wherein the control device (32) is configured to calculate the braking torque, and wherein the spatially resolved result of the current flowing between the brake disc (4) and the brake pads (6) is taken into account when calculating the braking torque.

9. A method for determining the braking torque of a brake (2) having a brake disc (4) and brake pads (6), comprising the following steps a. Apply voltage between the brake disc (4) and the brake pads (6), b. Determine the multiple currents currently flowing between the brake disc (4) and the brake pads (6), each current being associated with an electrical contact point (8) of the brake pads (6). c. Determine the current effective friction radius of the brake (2) using the determined current. d. Determine the current braking pressure of brake (2), e. Determine the current coefficient of friction between the brake pad (6) and the brake disc (4), or f. Determine the current braking torque based on the determined current braking pressure, the friction characteristic diagram of the brake (2) stored in the memory, and the determined current effective friction radius.

10. A motor vehicle having a brake (2) according to any one of claims 1 to 5, a braking system according to any one of claims 6 to 8, or a control device (24) configured to perform the method according to claim 9.

Images