Temperature warning for service brake system in a motor vehicle

Abstract

The invention relates to a system for a vehicle for warning a driver of the vehicle of overheating of the brakes, comprising a temperature sensor (1) for determining a current temperature at at least one brake of the vehicle and a computing unit (3) and an output unit (5), characterized in that the computing unit (3) is configured to issue a first warning to the driver of the vehicle by means of the output unit (5) upon reaching a first criticality condition, depending on the current temperature and a gradient of the current temperature, and to issue a second warning to the driver by means of the output unit (5) upon reaching a second criticality condition, wherein the first warning is replaced when the second warning is issued.

Description

[0001] The invention relates to a system for a vehicle to warn a driver of the vehicle of overheating of the brakes, and to a method for a vehicle to warn a driver of the vehicle of overheating of the brakes.

[0002] Various boundary conditions must be considered when designing a vehicle's mechanical braking system. One of the most important design criteria is the temperature capacity of a brake disc. During braking, heat is generated by the friction work required for braking; the brake disc is subjected to particularly high thermal stress during long downhill stretches. If the brake disc reaches an excessively high temperature, the overall efficiency of the braking system is significantly reduced, resulting in brake fade. Conventional brake design focuses on massing the brake disc to ensure sufficient heat capacity. However, this often results in a high component weight.

[0003] With the electrification of motor vehicles, the average vehicle curb weight has increased significantly due to the weight of the electrical components. Weight reduction is therefore of paramount importance. With the electrification of the drive system, regenerative braking is a crucial component of the energy efficiency strategy. In this process, the vehicle's kinetic energy is converted into electrical energy in the electric drive motor and typically fed back into the traction battery. During regular operation of a battery-electric vehicle on flat terrain, a very high proportion of braking is handled by this regenerative braking. This means that the mechanical braking system is hardly used during normal vehicle operation, and the brake disc temperature remains very low. Therefore, it is possible to design the component geometry to minimize component weight.

[0004] Battery-electric vehicles typically utilize regenerative braking, which reduces the weight of the mechanical braking system. This allows the mechanical braking system to be smaller, as it is expected to generate less heat. However, there are exceptions, such as long downhill stretches. If the electric vehicle's traction battery is fully charged before departure, it cannot absorb the energy generated by recuperation. In this case, only the mechanical braking system is used for deceleration and is subjected to high thermal stress.In a typical vehicle with an internal combustion engine, the engine's drag torque can be used to assist the mechanical braking system, whereas in an electric vehicle, a comparable function is only possible if the battery has sufficient energy absorption capacity.

[0005] A warning system can be provided for the driver, which issues a warning when a critical brake disc temperature of the mechanical braking system is reached and requires an adjusted driving style. This warning typically occurs in two stages: The first stage is a warning about the high temperature; this requires more cautious driving. This warning is advantageously triggered when a defined temperature is reached, at which point no loss of friction (fading) of the braking system has yet occurred (Warning Temperature 1). The second stage of the warning sequence is advantageously triggered after a further increase to an even higher specified temperature, at which point, although no fading has yet occurred, the driver must promptly stop the vehicle (Warning Temperature 2).There is a safety margin between these two temperatures, so that by driving more cautiously after the first warning, the driver will normally not reach warning temperature 2. However, with current technology, it can happen that the time between the first and second warnings is too short to avoid reaching warning temperature 2.

[0006] DE 3940456 A1 relates to a method for warning of and preventing overloading of the brakes of a motor vehicle with an internal combustion engine and sensors assigned to individual wheel brakes for detecting the instantaneous temperature of at least one functionally essential brake component per wheel brake, wherein: detected temperature values ​​are subjected to a limit value test, detected temperature values ​​are subjected to a trend evaluation, for this purpose a time average of detected temperature values ​​is calculated, the gradient of the aforementioned average is calculated, the average and a measure T_S proportional to the gradient of the average are linked together, the result of the linkage is compared with a fixed limit value T_G, which represents the maximum temperature level when the maximum permissible braking power is fully utilized.and wherein, after reaching or exceeding the limit value T_G, a status signal U_S is triggered, at least to issue an alarm. In this DE 3940456 A1, the monitoring of the brake temperature with the calculated forecast is described accordingly. The measured temperature and its temporal gradient are recorded and compared with the defined limit temperature. According to the disclosure, this forecast is used to control the powertrain unit of an internal combustion engine vehicle, so that the braking load is reduced by the powertrain. However, this method only considers the limit temperature and does not provide an early warning (the first stage of the common warning system). The limit temperature is fixed.

[0007] DE 10 2015 105 862 A1 further relates to a method for increasing the operational reliability of thermally stressed functional components of a disc brake, wherein the temperatures are detected by at least one sensor and transmitted as signals to an evaluation unit for a target-actual comparison, whereby controllable functional components are readjusted according to the determined deviations from target values. Thus, while monitoring of the brake disc temperature and readjustment of controllable functional components such as the service brake by applying brake pressure when the brake disc temperature is too high is described, a warning to a driver is not provided.

[0008] CN 115534919 A ​​also relates to a method for monitoring the temperature of a vehicle's braking system, which includes: determining a dynamic warning temperature curve for the braking system, wherein the dynamic warning temperature curve is based on the warning temperature value of the braking system and a threshold value indicating the number of times the warning temperature value is exceeded by the braking system temperature; monitoring the frequency with which the temperature of this braking system exceeds the warning temperature value of the dynamic warning temperature curve; and, if the temperature exceeds the braking system threshold several times, adjusting the warning temperature of the dynamic warning temperature curve to a reduced warning temperature. Thus, in this CN 115534919 A, a critical temperature is lowered by monitoring when such a critical temperature is exceeded.This procedure aims to increase the safety margin by lowering the warning temperature; in this application, the frequency of exceeding the limit temperature is used.

[0009] Reducing the first warning temperature (warning temperature 1) unconditionally is not advisable, as this would trigger an unnecessary warning when the battery-electric vehicle has a low operating weight, such as when it is empty.

[0010] DE 102 59 529 B4 relates to a method for determining the brake condition of a motor vehicle brake using a temperature sensor arranged in or on a brake pad. The brake condition of the motor vehicle brake, which is in particular a disc brake, is determined using the temperature measured by the temperature sensor. This involves evaluating the temperature over time: In addition to a first temperature value, at least one second temperature value measured after the first, and the time interval between the measurement times of the two temperature values, are taken into account.

[0011] DE 102 43 127 A1 relates to the use of an inductive signal transmitter designed to detect the position, displacement, angular position, or rotational speed of a moving element for generating a signal for the temperature of one or more components located in the vicinity of the signal transmitter. This results in a cost-effective integration of functions in a single assembly.

[0012] DE 10 2016 004 804 A1 relates to a method for operating a motor vehicle powered solely by at least one electric machine, wherein electrical energy for supplying the at least one electric machine is stored in at least one electrical energy storage device, wherein the motor vehicle has at least one hydraulic brake, wherein, in the event that the motor vehicle is traveling downhill and / or the at least one hydraulic brake is actuated for a definable period of time, at least one of several measures is taken, wherein in a first measure the at least one hydraulic brake is cooled and wherein in a second measure recuperation is carried out, whereby mechanical energy of the motor vehicle is converted into electrical energy and stored in the at least one electrical energy storage device.

[0013] DE 42 14 181 A1 relates to a method for brake pad wear control in the sense of compensating for differences in brake pad wear in a pressure-medium-actuated motor vehicle braking system with a service brake valve and downstream solenoid valves, with a wear sensor for detecting the respective wear of a brake pad on each wheel of the axles, wherein the output signals of the wear sensors are supplied to a control electronics which, in the case of different wear of the brake pads, generates signals for controlling the solenoid valves by means of which the brake pressures at the wheel brakes are controlled, described.in which a further brake pad wear value is determined indirectly from physical state variables of the sensed and non-sensed wheel of the same axle during braking, and the larger of the two directly measured and indirectly determined brake pad wear values ​​is used as the actual brake pad wear value for the control system.

[0014] The object of the invention is to improve the handling of longer braking processes in a motor vehicle, in particular a battery-electric vehicle.

[0015] The invention is defined by the features of the independent claims. Advantageous further developments and embodiments are the subject of the dependent claims.

[0016] A first aspect of the invention relates to a system for a vehicle for warning a driver of the vehicle of brake overheating, comprising a temperature sensor for determining a current temperature at at least one brake of the vehicle, a processing unit, and an output unit, wherein the processing unit is configured to issue a first warning to the driver of the vehicle via the output unit upon reaching a first criticality condition, depending on the current temperature and a gradient of the current temperature, and to issue a second warning to the driver via the output unit upon reaching a second criticality condition, wherein the first warning is replaced upon issuance of the second warning, and wherein the processing unit is further configured to check whether the temperature exceeds a respective criticality condition only when a gradient is exceeded above a predetermined gradient threshold.

[0017] An electric vehicle can typically assist braking during a long downhill stretch through electrical recuperation, thereby relieving the vehicle's mechanical braking system. By incorporating this electrical braking, the mechanical brake disc can be designed with a lower mass. However, there are situations in which recuperation does not occur due to a fully charged battery. Even in critical situations, the system limits the driver's safety margin to the level of the previous limit case.

[0018] The first warning and the second warning thus describe escalation levels, with the first warning preferably being understood as a suggestion, the second warning in particular as a strict request to stop immediately.

[0019] Advantageously, this provides a method that issues a timely warning to the driver of a battery-electric vehicle for safe downhill driving, without causing unnecessary warnings. In a critical situation regarding battery fading (e.g., during a long downhill drive with a fully charged battery), the driver of an electric vehicle is informed early about the situation by means of the first criticality condition, so that the driver's reaction time remains at the level of a conventional combustion engine vehicle.

[0020] According to an advantageous embodiment, the temperature sensor serves to determine a temperature on a brake disc of at least one brake of the vehicle.

[0021] According to an advantageous embodiment, the first criticality condition specifies a first minimum period until a limit temperature is reached at the at least one brake, wherein the second criticality condition specifies a second minimum period until the limit temperature is reached at the at least one brake, wherein the first minimum period is longer than the second minimum period.

[0022] In particular, the limit temperature is predefined and static. Alternatively, two limit temperatures can be specified, and a first minimum period until reaching the first limit temperature and a second minimum period until reaching the second limit temperature can be determined.

[0023] According to an advantageous embodiment, the first criticality condition is the reaching of a first limit temperature by the temperature determined by the temperature sensor at the at least one brake, wherein the second criticality condition is the reaching of a second limit temperature by the temperature determined by the temperature sensor at the at least one brake, wherein the computing unit is designed to determine at least the first limit temperature as a function of the gradient.

[0024] The first warning to the driver specifically advises cautious driving, suggesting, for example, intermittent braking, a generally lower average speed, or a break to prevent further increases in brake temperature, particularly of the brake disc, and ideally even to reduce it. The second warning from the display unit, however, urges the driver to stop immediately, as the second temperature is higher than the first, indicating imminent brake fade and a resulting loss of braking power. This is a safety hazard, and allowing the brakes to cool down is absolutely essential.In other words, the first warning indicates a more distant exceedance of the maximum permissible brake temperature and calls for prompt consideration of this during driving, for example by taking a break, or by adjusting driving behavior, while the second warning indicates a more recent exceedance of the maximum permissible brake temperature and urges immediate or prompt consideration of this during driving (break) or driving behavior.

[0025] The processing unit thus uses not only the first limit temperature as a static value, but also incorporates the current temperature gradient of the brake for issuing the first warning. There are essentially two ways to implement this: Firstly, the processing unit can dynamically determine the first limit temperature, i.e., its value can be determined based on the gradient. This can be done using a predefined function of the processing unit. Secondly, it can calculate whether, given the current brake temperature and gradient, the first limit will be reached in the near or distant future, if at all.Accordingly, the first warning can be issued sooner or later, depending on whether the brake is expected to reach the first limit temperature in the near future or not.

[0026] According to a further advantageous embodiment, the computing unit is designed to determine the second limit temperature depending on a temperature gradient.

[0027] According to a further advantageous embodiment, the computing unit is designed to determine the gradient by means of a current temperature measurement and a past temperature measurement at the brake and a time interval between the current measurement and the past temperature measurement.

[0028] According to another advantageous embodiment, the computing unit is designed to calculate the gradient using an energy model.

[0029] Using the energy model, the processing unit is able to predict the future temperature state of at least one brake. A brake temperature simulation model can be used for this purpose: This model simulates the thermal state of the brake disc based on vehicle operating information such as brake pedal position, brake fluid pressure, speed, etc. If the vehicle can be equipped with at least one temperature sensor, this sensor information can replace the simulation model. The gradient of the disc temperature is then calculated using this temperature information. Furthermore, the battery's state of charge and / or a measured or estimated vehicle load can be taken into account, with the vehicle load being determined, for example, by a vehicle stability control unit.

[0030] According to a further advantageous embodiment, the energy model takes into account at least one of the following current values: current recuperation capacity of the vehicle, estimated or measured load of the vehicle, braking force, braking duration, previous and / or current number of individual braking maneuvers on the vehicle.

[0031] The current recuperation capacity can refer, on the one hand, to the current maximum available charging power of the vehicle's battery, thus indicating the maximum amount of braking energy that the battery of the battery-electric vehicle can currently absorb and convert into electrical energy; on the other hand, it can refer to the current state of charge of the battery, since as the state of charge increases, the remaining amount of energy that the battery can still absorb after conversion from braking energy decreases. Both aspects can also be taken into account in the current recuperation capacity.

[0032] According to a further advantageous embodiment, the computing unit is designed to execute the first warning and the second warning differently by means of the output unit, visually and / or audibly and / or haptically.

[0033] The differences between the first and second warnings can be achieved through different text formatting such as fonts, font colors, font sizes, as well as through different symbols or differently colored symbols and different warning tones.

[0034] According to a further advantageous embodiment, the computing unit is designed to check whether the temperature exceeds the first limit temperature only when a battery charge level above a predetermined charge level threshold is exceeded.

[0035] According to the invention, the computing unit is designed to check whether the temperature exceeds a respective criticality condition only when a gradient exceeds a predetermined gradient threshold.

[0036] Another aspect of the invention relates to a method for a vehicle to warn a driver of the vehicle of brake overheating, wherein a temperature sensor determines the current temperature at at least one brake of the vehicle, a processing unit determines a temperature gradient, depending on the current temperature and the gradient of the current temperature, a first warning is issued to the driver of the vehicle by means of the output unit upon reaching a first criticality condition, and a second warning is issued to the driver by means of the output unit upon reaching a second criticality condition, wherein the first warning is replaced when the second warning is issued, and wherein the processing unit only checks whether the temperature exceeds a respective criticality condition when a gradient is exceeded above a predetermined gradient threshold.

[0037] Advantages and preferred further developments of the proposed procedure result from an analogous and substantive transfer of the above statements made in connection with the proposed system.

[0038] Further advantages, features and details will become apparent from the following description, in which - possibly with reference to the drawing - at least one embodiment is described in detail.

[0039] They show: Fig. 1: A vehicle with a system for warning the driver of the vehicle of overheating of the brakes according to an embodiment of the invention. Fig. 2: A situation for applying the system of Fig. 1 according to an embodiment of the invention. Fig. 3: A method for warning a driver of the vehicle of overheating of the brakes according to an embodiment of the invention.

[0040] The representations in the figures are schematic and not to scale.

[0041] Fig. Figure 1 shows a vehicle equipped with a system to warn the driver of brake overheating. The system typically activates during long downhill stretches; during normal operation on level ground, the system will typically not activate, as prolonged braking that could heat at least one brake to a temperature approaching brake fade is highly unlikely. However, during extended downhill stretches, particularly with a trailer and / or full load, but also with an empty vehicle if the descent is sufficiently long and steep, temperatures at least one brake can reach such a high level that a warning to the driver is warranted. A two-stage warning scheme is employed by a processing unit 3 in the vehicle to transmit the relevant information to the driver via an output unit 5.For this purpose, the processing unit 3 receives current temperature values ​​from a temperature sensor 1 on at least one brake of the vehicle. As a first warning, the driver is shown a symbol, preferably in orange, with text and information that at least one brake of the vehicle has reached such a high temperature that the driver should take a break or adjust their driving style. Only with a second warning, which is issued when the at least one brake reaches an even higher temperature, critically high enough to cause brake fade (i.e., a loss of braking power), is the driver preferably prompted by a red symbol and an explicit fault message to stop immediately in order to prevent the temperature of the at least one brake from increasing further and to ensure that sufficient braking power remains available for the vehicle.At least for calculating a first threshold temperature, at which the first warning is issued by processing unit 3 to output unit 5, the gradient is calculated based on a previously calculated gradient. The gradient describes the time derivative of a substantially current temperature of the at least one brake and thus indicates a current change, in particular an increase, in the temperature of the at least one brake. Preferably, processing unit 3 continuously checks whether the current temperature of the at least one brake exceeds a first threshold value, for example, 400°. If this is the case, the temperature gradient is used to calculate the first threshold temperature, in particular using the following formula: T_(warn1)=T_0−(degree−1°C / s)*100s

[0042] In this formula, T_(warn1) is the first limit temperature, T_0 is a predefined temperature constant, and 'degrees' is the current gradient in degrees Celsius per second. If a gradient of 2°C / s of temperature increase is determined at at least one brake using this formula, and 500°C is chosen as an example for T_0, then the first limit temperature T_(warn1) is calculated to be 400°C. If the gradient increases, this means that the temperature at at least one brake is rising even faster, and the first limit temperature will therefore be lower in order to provide an earlier initial warning to the driver. However, the smaller the gradient, the higher the first limit temperature can be, since a critically higher temperature leading to brake fade will be reached significantly later.This evaluation using the gradient can also be conditional, in particular depending on whether the battery charge level is above a first threshold and / or the current brake temperature is above a second threshold; in addition, the first limit temperature can be made dependent on the vehicle's load level.

[0043] Fig. Figure 2 shows an example situation with a vehicle on a downhill slope, which is equipped with the system as described below. Fig. The vehicle is equipped as described in section 1. Initially, the vehicle is on a hill with a relatively high battery charge, followed by a descent. First, the mechanical braking system is supported by electrical recuperation as long as the battery can still absorb sufficient electrical power and increase its charge. Once the battery is fully charged, braking must be performed solely by the mechanical braking system. If the temperature of at least one brake rises to 600 °C, the first temperature limit, determined based on a previously calculated temperature gradient of the brake temperature increase, is reached, and the driver receives a first warning. If the second temperature limit of 700 °C is actually reached, the driver receives a second warning, at which point they can interrupt their journey and resume it when the temperature falls below the first limit of 600 °C.

[0044] Fig. Figure 3 shows a method for a vehicle to warn a driver of the vehicle of brake overheating, wherein a temperature sensor 1 determines a current temperature at at least one brake of the vehicle S1, a temperature gradient is determined by a computing unit 3 S2, depending on the current temperature and the gradient of the current temperature, a first warning is issued to the driver of the vehicle by means of the output unit 5 upon reaching a first criticality condition S3 and a second warning is issued to the driver upon reaching a second criticality condition by means of the output unit 5 S4, whereby the first warning is replaced when the second warning is issued.

[0045] Although the invention has been further illustrated and explained in detail by means of preferred embodiments, the invention is not limited by the disclosed examples, and other variations can be derived from them by a person skilled in the art without departing from the scope of protection of the invention. It is therefore clear that a multitude of possible variations exist. It is also clear that the embodiments mentioned as examples are truly only examples and are not to be understood in any way as limiting, for example, the scope of protection, the possible applications, or the configuration of the invention.Rather, the preceding description and the description of the figures enable the person skilled in the art to implement the exemplary embodiments in concrete terms, whereby the person skilled in the art, with knowledge of the disclosed inventive concept, can make various changes, for example with regard to the function or the arrangement of individual elements mentioned in an exemplary embodiment, without leaving the scope of protection defined by the claims and their legal equivalents, such as further explanations in the description.

Images