Braking device and method for uniform braking

Abstract

Braking device (1) of a rail vehicle, comprising a brake actuator (5) and a brake pad (6) which can be moved thereby, as well as a brake disc (7) which interacts therewith and is connected in a rotationally fixed manner to a wheel (8), for generating a braking force which slows down the rail vehicle in response to a braking request from an electronic control unit (2), wherein the braking force is dependent on the normal force (16) generated by pressing the brake pad (6) onto the brake disc (7) and on a factor which depends on the relative speed (17), material (12;13) and temperature of the brake pad and the brake disc, wherein the control unit (2) has a computing unit (3) which, in response to a braking request, modulates the normal force curve (22) over time in order to generate a target braking force curve, characterized in that at least one braking parameter curve is stored in the control unit (2), which is based on a friction coefficient curve (15) which arises when braking from an initial speed to a target speed with a constant normal force (16) and a combination of test bench parameters (14), and that the modulation of the normal force takes place in accordance with the at least one braking parameter curve.

Description

[0001] The present invention relates to a braking device for a rail vehicle, comprising a brake actuator and a brake pad movable thereby, as well as a brake disc interacting therewith, which is non-rotatably connected to a wheel, for generating a braking force that slows down the rail vehicle in response to a braking request from an electronic control unit, wherein the braking force is generated as a function of the normal force generated by pressing the brake pad onto the brake disc and of a coefficient of friction which depends on the relative speed, material and temperature of the brake pad and the brake disc.

[0002] Furthermore, the invention also relates to a method for providing a braking device according to the invention and a method for operating it.

[0003] The invention applies to rail vehicles where braking is achieved by an actuator pressing a brake pad against a brake disc, for example, one attached to a wheel or the wheel axle. The actuator thus directly exerts a normal force, i.e., a force perpendicular to the surface of the brake disc, which is then converted into a braking force by the friction between the brake pad and the brake disc. The coefficient of friction mediates between the normal force and the braking force. A higher coefficient of friction results in a higher braking force.

[0004] It is desirable to be able to make the most accurate possible predictions about the braking behavior of a rail vehicle, or to ensure that the braking process of a rail vehicle is as controlled as possible. In particular, there are regulations that specify, for example, the maximum braking deceleration of passenger trains. Since the means used for braking is the brake pad, and especially the normal force of the brake pad on the brake disc is specified, it is desirable to be able to make statements about the coefficient of friction of a brake consisting of a brake pad and brake disc.

[0005] To brake a rail vehicle, a control pressure is applied by a train driver in generally known prior art and controlled via an actuating device to initiate a braking process. This generates a normal force, for example, by a pneumatically, hydraulically, or electromechanically driven actuator, which presses a brake pad against a brake disc that is fixed to a wheel. A braking force is then mediated by a coefficient of friction, which acts on this wheel. The final braking force also depends on the ratio of the brake disc size to the wheel size. In particular, models used in conventional prior art braking systems assume a constant coefficient of friction over time. This is typically, for example, between 0.3 and 0.4.

[0006] WO 2010 / 069520 A2 describes a braking system of a type for a rail vehicle in which various measurements are taken by additional sensors on the wheel or wheelset of the rail vehicle to control a uniform braking process. The main disadvantage of this is the additional sensors that must be installed and evaluated on such a train.

[0007] WO 2013 / 034693 A2 describes a control device for the braking system of a rail vehicle. To reduce the required number of sensors, the braking force exerted during braking is determined based on the brake pressure or braking current and another parameter. Test braking can be performed for this purpose. Based on the determined data, the braking system is controlled to achieve the specified braking effect. A disadvantage of this method is that environmental influences, such as the temperature of the brake disc or wheels, are not taken into account.

[0008] German patent application DE 10 2011 111 589 A1 discloses a braking device for a vehicle, specifically a road vehicle. Prior to braking, the dependencies of the applied braking torque on the applied brake pressure are taken into account. For this purpose, a data storage device is provided in which relevant values ​​relating to the dependence of the braking torque exerted by the brake pads and the brake disc are stored. These values ​​stored in the data storage device, which are accessed before braking, can be determined either theoretically or empirically through corresponding test series. The temperature can also be recorded using a temperature model. Additionally, the dependence of the braking torque or the coefficient of friction on various influencing factors is disclosed. The corresponding values ​​can be stored in a matrix.

[0009] State of the art DE 199 43 352 A1 discloses the application of a temperature model specifically for a rail vehicle.

[0010] The object of the present invention is to create a braking device for a rail vehicle that enables a uniform braking force profile with minimal sensor effort.

[0011] The problem is solved starting from a braking device according to the preamble of claim 1 in conjunction with its characterizing features. The following dependent claims describe advantageous embodiments of the invention. Two methods relating to the invention are presented in claims 11 and 12.

[0012] The invention includes the technical teaching that at least one brake parameter profile is stored in the control unit, which is based on a coefficient of friction profile that arises during deceleration from an initial speed to a target speed with constant normal force and a combination of test bench parameters, and that the modulation of the normal force is carried out according to the at least one brake parameter profile.

[0013] In a preferred special case, the target speed is zero. This corresponds to the frequently occurring case of emergency braking or rapid braking.

[0014] The advantage of the braking device according to the invention lies particularly in the fact that the modulation of the normal force is not carried out based on sensor data acquired simultaneously or during operation, but primarily based on previously defined coefficient of friction profiles, for example, recorded in a test rig such as a flywheel test rig. For example, the coefficient of friction of the brake pad and brake disc of a model corresponding to the rail vehicle may have been recorded in a test rig, and this coefficient of friction profile may have been stored in the control unit. Then, during operation, i.e., outside the test rig, it is possible to compensate for fluctuations in the coefficient of friction, which arise, for example, from heating of the brake pad or brake disc or other effects, by, for example, modulating the normal force of the actuator that actuates the brake pad in the opposite direction.

[0015] According to a measure improving the invention, the brake parameter curve based on the coefficient of friction corresponds to the calculated curve of the normal force that must be generated by the actuator to produce the desired target brake force curve. Alternatively, and also preferably, it is possible that the coefficient of friction curve itself is stored on the control unit, so that the electronic processing unit of the control unit can calculate or estimate the necessary normal force during operation based on the stored coefficient of friction curve.

[0016] According to an advantageous embodiment of the invention, the target braking force profile is largely constant over time. This makes it particularly easy to comply with legal regulations, for example. In particular, assuming ideal traction utilization, i.e., slip-free movement of the wheels over the rail, this also results in a constant braking acceleration or deceleration of the train or rail vehicle over time.

[0017] An advantageous embodiment of the invention provides that the brake parameter profile is assigned to a combination of test bench parameters. The advantage here is that this assignment allows the selection of a brake parameter profile by specifying the test bench parameters associated with the respective profile. For example, this assignment can be established through tests on a test bench or through numerical simulations.

[0018] A preferred embodiment of the invention provides that the brake parameter profile is stored as an entry in an n-dimensional test bench matrix, wherein each entry of the test bench matrix consists of a brake parameter profile and each entry is assigned to a combination of n test bench parameters. Thus, during driving, for example, the parameters used in the test bench that most closely match the current parameters present during driving can be selected in order to choose a suitable entry from the test bench matrix. Based on this entry, which consists of a brake parameter profile containing, for example, the normal force or the braking value, a corresponding modulation of the normal force can then be initiated, thereby generating the desired target brake force profile.Each dimension of this test bench matrix can refer to a discrete gradation of a continuous value, such as an initial velocity, or to a few discrete parameters, such as the material of the brake pad or the material of the brake disc.

[0019] An advantageous embodiment of the invention provides that the processing unit for modulating the normal force interpolates between the entries of the matrix and / or extrapolates beyond them. Thus, if a braking parameter profile is to be selected for a combination of parameters that are not explicitly stored in the test bench matrix in exactly this way, a braking parameter profile usable in accordance with the invention can nevertheless be calculated by interpolation.

[0020] An improvement of the invention includes the ability to calculate the brake parameter profile as a function of test bench parameters. An electronically stored function can accept the test bench parameters as arguments and deliver a brake parameter profile as a calculation result, for example, via interpolation implemented in the function.

[0021] Advantageously, the test bench parameters are contained in a test bench parameter group, which includes, among other things, the initial speed of the rail vehicle, the final speed of the rail vehicle, the initial rotational speed of the wheel, the diameter of the wheel, the effective diameter of the brake disc, the normal force, the brake disc material, the brake pad material, the mass of the rail vehicle, the initial kinetic energy of the rail vehicle, the initial momentum of the rail vehicle, the initial temperature of the brake pad, the initial temperature of the brake disc, the ambient temperature of the wheel, the duration of the braking process, and the time and duration of at least the last braking action, as well as other relevant parameters as needed. The effective diameter corresponds to twice the distance from the axle or shaft of the wheel at which the brake pad effectively interacts with the brake disc.

[0022] All these parameters can be measured on a test bench and are relevant for the shape of the coefficient of friction curve and the resulting normal force curve. While the initial temperature of the brake pad and the initial temperature of the brake disc cannot be measured in conjunction with the brake device according to the invention without additional sensors, the known ambient temperature can, for example, be selected as the initial temperature for the brake disc and brake pad. Furthermore, the current temperature can be estimated by knowing the previous braking cycles.

[0023] A further improvement of the invention provides that the processing unit calculates the temperature of the brake disc and / or the brake pad. Such a calculation would be performed using a temperature model that takes into account material properties and structural properties, particularly of the brake disc. Thus, for example, by knowing the ambient temperature and the braking cycles performed to date, a temperature of the brake disc and / or brake pad can be calculated in order to select the most suitable entry from the test bench matrix.

[0024] A method for generating at least one friction coefficient curve for storing it in the control unit, i.e., for programming it, involves measuring the friction coefficient curve of a brake disc and a brake pad in a flywheel test rig while the normal force of the brake pad on the brake disc is constant. By performing this measurement for various test parameters, such as the initial and final speed of the train, its mass, the rotational speed of the wheels, and the material of the brake pad and brake disc, a test rig matrix can be created which, according to the invention, eliminates the need for measurements of, for example, temperature or braking force during operation.

[0025] A method concerning the operation of the braking system provides that the normal force of the brake pad on the brake disc is modulated over time according to a braking parameter profile, which is selected from a test bench matrix based on instantaneous parameters. Ideally, this generates a target braking force profile, in particular a braking force profile that remains constant over time.

[0026] Further measures improving the invention are described in more detail below, together with a description of a preferred embodiment of the invention, with reference to the figures. The figures show... Fig. 1 a scheme of a braking device according to the invention, Fig. 2 a block diagram of a method according to the invention for operating the braking device, and Fig. 3 graphs for evaluating the operation of the braking system.

[0027] According to Fig. Figure 1 comprises a rail vehicle (not shown here) comprising a braking device 1, which in turn comprises a control unit 2, which in turn comprises a computing unit 3 and a storage unit 4. The braking device 1 further comprises a brake actuator 5 with a cooperating brake pad 6, which can be normally pressed against the brake disc 7 of a wheel 8. Further optional brake actuators, brake pads, and brake discs, which may, for example, interact with further optional wheels, are not shown.

[0028] The processing unit also communicates with a speed sensor 9 and a temperature sensor 10, which record the train's speed and the ambient temperature near the braking device 1. Together with information stored in the storage unit 4 about the train mass 11 or the mass proportional to the braking device 1, the brake pad material 12, and the brake disc material 13, the processing unit is thus able to query a coefficient of friction 15 from a test bench matrix 14 stored in the storage unit 4. This coefficient of friction was previously measured in a test bench where braking was performed under similar or identical parameters with a constant normal force applied to a brake pad 6 on a brake disc 7.

[0029] Knowing this coefficient of friction profile 15, the normal force can now be modulated over time, resulting in a constant braking force profile. In particular, this braking device does not have a brake force sensor or a measuring device for determining the coefficient of friction.

[0030] Fig. Figure 2 illustrates this process in a block diagram. The input values ​​for calculating, querying, or interpolating the coefficient of friction curve 15 are the normal force 16 present at the beginning of the braking process, the speed 17 of the brake disc 7, the ambient temperature 18, and the kinetic energy 19 of the train. In an estimator module 20, a corresponding coefficient of friction curve 15 is queried or, for example, interpolated or extrapolated from a test bench matrix 14 (not shown here), which was measured in a flywheel test bench under appropriate parameters. This coefficient of friction curve 15, i.e., the time-dependent coefficient of friction, is then passed to a temperature module 21, which uses it to calculate the temperature, particularly of the brake disc 7. This temperature is optionally passed back to the estimator module 20 for a more precise determination of the coefficient of friction curve 15, thus allowing for more reliable compensation of its fluctuations.From the calculated coefficient of friction profile 15, the ideal normal force profile 22 can then be determined, which must be applied to obtain a braking force that is as constant as possible. For example, an increasing normal force compensates for a decreasing coefficient of friction.

[0031] In Fig. Figure 3 shows three graphs illustrating the operation of a braking device 1 according to the invention during braking over a distance s, measured in meters, plotted on the horizontal axis.

[0032] Firstly, the coefficient of friction curve 15 is plotted at a constant normal force, as would occur, for example, in the prior art or as would be measured in a flywheel test rig. The value of the coefficient of friction curve 15 corresponds to one-tenth of the value plotted on the right-hand axis. It can be seen, for example, how the coefficient of friction curve 15 initially decreases due to factors including heating, and then increases sharply towards the end of the braking process, mainly caused by the deceleration of the rail vehicle. This increase in the coefficient of friction towards the end of the braking process is typically also audibly perceptible.

[0033] A brake pressure curve 23, compensated according to the invention and plotted against the right axis, which indicates a pressure P in bar, or a corresponding normal force curve 22, compensated according to the invention (not shown here), therefore decreases towards the end of the braking process in order to compensate for the increase in the coefficient of friction curve 15. As a result, the braking deceleration or the acceleration 24 of the rail vehicle, plotted against the left axis, which indicates an acceleration a in m / s², is almost constant over the entire braking duration or the entire braking distance.

[0034] The invention is not limited to the preferred embodiment described above. Rather, variations thereof are also conceivable, which are also covered by the scope of protection of the following claims.

[0035] For example, it is also possible that the brake parameter curves are not stored as curves with a number of data points, but as analytical functions, such as Fourier series or Taylor series. Furthermore, the brake parameter curves can be stored differently than in a matrix, for example as a function, so that a brake parameter curve can be calculated from a combination of test bench parameters.

[0036] The brake actuator can also operate pneumatically, electromechanically or hydraulically, and the brake disc can be mounted on an axle or wheelset shaft of the wheel instead of on the wheel itself. Reference symbol list 1. Braking system 2 Control unit 3 Computing Unit 4 storage units 5 Brake actuator 6 brake pads 7 brake disc 8 wheel 9 Speed ​​sensor 10 Temperature 11 Train mass 12 Brake pad material 13 Brake disc material 14 Test bench matrix 15 Friction coefficient curve 16 Normal force 17 Speed 18 Ambient temperature 19 kinetic energy 20 Estimator Module 21 Temperature module 22 Normal force curve 23 Brake pressure curve 24 Acceleration

Claims

[1] Braking device (1) of a rail vehicle, comprising a brake actuator (5) and a brake pad (6) movable thereby, as well as a brake disc (7) interacting therewith and non-rotatably connected to a wheel (8), for generating a braking force to slow down the rail vehicle in response to a braking request from an electronic control unit (2), wherein the braking force is generated as a function of the normal force (16) generated by pressing the brake pad (6) against the brake disc (7) and of a coefficient of friction which depends on the relative speed (17), material (12; 13) and temperature of the brake pad and the brake disc, wherein the control unit (2) has a processing unit (3) which, in response to a braking request, modulates the normal force profile (22) over time in order to generate a target braking force profile, characterized by, that at least one brake parameter profile is stored in the control unit (2) which is based on a coefficient of friction profile (15) which arises when decelerating from an initial speed to a target speed with constant normal force (16) and a combination of test bench parameters (14), and that the modulation of the normal force is carried out according to the at least one brake parameter profile. [2] Braking device (1) according to claim 1, characterized by , that the brake parameter curve based on the coefficient of friction curve (15) corresponds to the normal force curve (22), which generates the target brake force curve. [3] Braking device (1) according to claim 1 characterized by , that the brake parameter curve based on the friction coefficient curve (15) corresponds to this friction coefficient curve (15). [4] Braking device (1) according to any one of the preceding claims, characterized by that the target braking force curve is constant over time. [5] Braking device (1) according to any one of the preceding claims, characterized by , that the brake parameter curve is assigned to a combination of test bench parameters. [6] Braking device (1) according to claim 5, characterized by , that the brake parameter profile is stored as an entry in an n-dimensional test bench matrix (14), wherein each entry of the test bench matrix consists of a brake parameter profile, and each entry is assigned to a combination of n test bench parameters. [7] Braking device (1) according to claim 6, characterized by , that the computing unit (3) interpolates between entries of the matrix for modulating the normal force profile (22) and also extrapolates beyond that. [8] Braking device (1) according to claim 5, characterized by , that the brake parameter curve can be calculated as a function of test bench parameters. [9] Braking device (1) according to any one of the preceding claims, characterized by, that the test bench parameters are included in a test bench parameter group to which the initial speed of the rail vehicle, the final speed of the rail vehicle, the initial rotational speed of the wheel (8), the diameter of the wheel (8), the effective diameter of the brake disc (7), the normal force (16), the brake disc material (13), the brake pad material (12), the mass (11) of the rail vehicle, the initial kinetic energy (19) of the rail vehicle, the initial momentum of the rail vehicle, the initial temperature of the brake pad (6), the initial temperature of the brake disc (7), the ambient temperature (18) in the area of ​​the braking device (1), the duration of the braking process and the time and duration of at least the last braking are assigned. [10] Braking device (1) according to any of the preceding claims, characterized by, that the computing unit calculates the temperature of the brake disc (7) using a temperature model with the help of a temperature module (21). [11] Method for determining at least one coefficient of friction curve (15) for storing it in a storage unit (4) of a control unit (2) of a braking device (1) according to one of claims 1 to 10, wherein the coefficient of friction curve (15) of a brake disc (7) and a brake pad (6) is measured at constant normal force (16) during at least one braking test on a vehicle-simulating test device. [12] Method for operating a braking device (1) according to one of claims 1 to 10, wherein a braking parameter profile is determined from a test bench matrix (14) in response to a braking request.

Images