Tire pressure monitoring system in motor vehicles

Abstract

A tire pressure monitoring system in a vehicle comprising at least one sensor for detecting the outside temperature (TA) and a sensor device on each wheel, which transmits at least the current tire pressure (P) and the current tire temperature (T) of the respective wheel to an evaluation device (1) permanently arranged in the vehicle, wherein the evaluation device (1) stores at least the respective tire pressure (P_init(T_init)) and the current outside temperature (TA_init) as initialization values ​​(INI) during an initialization process, records their current values ​​(P(T), TA) during driving and, within the framework of an air loss monitoring function (5) and within the framework of a separate outside temperature-dependent load capacity monitoring function (3), initiates the output of at least one pre-warning (W1) via an output unit (2),when the current tire pressure (P(TA)) converted to the current outside temperature (TA) falls below a predetermined threshold (P_W1), whereby the decreasing load-bearing capacity of the tire with decreasing outside temperature (TA) is taken into account when defining the threshold, characterized in that the evaluation device (1) furthermore, within the framework of the air loss monitoring function (5), initiates an immediate main pressure loss warning (W2) via the output unit (2) when a predetermined threshold (P_W2(TEMP)) requires the immediate main pressure loss warning (W2).

Description

[0001] The invention relates to a tire pressure monitoring system in motor vehicles according to the preamble of claim 1.

[0002] Such a system is known, for example, from DE 41 29 554 A1 or DE 195 32 386 A1 of the applicant. Such systems have, in particular, sensor devices inside the tire of each wheel. These sensor devices detect, for example, the air pressure and / or temperature inside the tire, convert these physical quantities into a corresponding voltage, and transmit this information to a stationary evaluation device located in the vehicle. This information transmission preferably takes place wirelessly via transponders.

[0003] For example, if the information "tire pressure" and "temperature" is transmitted to the evaluation device, the evaluation device compares the tire pressure with, for example, a minimum permissible threshold that depends on the temperature. If this minimum permissible threshold is undershot, the evaluation device can indicate to the driver which wheel has insufficient tire pressure. For this to work, the evaluation device must be informed at least once which sensor is assigned to which wheel. According to DE 195 32 386 A1, this assignment is made automatically in the system by means of a rotation direction sensor in the wheels in conjunction with a direction-of-travel detection system.

[0004] From EP 1 293 362 B1 of the applicant, a method for determining the tire air pressure and a tire stress parameter in the form of a so-called wheel load is also known, wherein the wheel load is determined from the tire contact patch measured by means of a deformation sensor.

[0005] Furthermore, DE 196 11 364 B4 describes a method and a device for vehicle tire monitoring with which a high level of tire operational safety can be achieved with minimal effort, DE 100 07 558 A1 describes a system for determining the target value of the tire air pressure with an evaluation unit for at least one driving value and environmental measurements, and US 2008 / 0042817 A1 describes a tire pressure management system with external, valve-mounted tire pressure sensors for a towing vehicle with a trailer.

[0006] The object of the invention is to improve a device of the type mentioned above in such a way that, on the one hand, a timely warning is issued, but premature warnings or false warnings are avoided.

[0007] This problem is solved by the features of claim 1. Advantageous further developments of the invention are the subject matter of the dependent claims.

[0008] The invention is based on the following considerations: The following warning strategy is generally the focus of current tire pressure monitoring systems: State of the art

[0009] Current tire pressure monitoring systems (TPMS) operate on the principle that a drop in pressure must always trigger a warning. The system measures the current tire pressure and compares it to a pressure threshold that is either pre-programmed into the system or previously confirmed by the driver as the correct pressure. The warning threshold at which a warning is issued is either mandated by legislation or set by the system manufacturer. Disadvantages of the state of the art

[0010] The legal requirement, in its testing procedure, assumes that the vehicle is parked in a previously conditioned state, the tire pressure is correctly set, and that external conditions, such as the outside temperature, barometric pressure, and load, can be considered constant during the functional test of the tire pressure monitoring system. Consequently, warning thresholds can be set very high in order to achieve other objectives, such as the fastest possible detection of a tire failure or the prevention of additional CO2 emissions due to increased rolling resistance.

[0011] In daily vehicle use, external conditions are not constant. To ensure optimal vehicle performance, the customer would have to check and readjust the tire pressure very frequently (every two weeks or whenever usage changes, as recommended in the owner's manual), and also ensure that the check is always performed when the tires are cold (i.e., initialization temperature equals ambient temperature). A temperature drop of approximately 25°C, which is quite common during transitional periods between morning and midday temperatures, triggers a warning that the customer cannot understand. This erodes trust in the system, which is counterproductive to the legislator's objective. Inventive measures

[0012] According to the invention, a warning strategy is proposed that separately identifies the various effects that can occur in a tire and displays their proportions and significance separately to the driver. This is achieved in conjunction with a sensor that can transmit at least the ambient temperature and preferably also the barometric pressure to the evaluation unit, which is already present for recording the tire pressure and temperature. This allows the load-bearing capacity of the tire (load-bearing capacity monitoring function, in particular a separate static monitoring function) to be evaluated, in addition to air loss (air loss monitoring function), at least as a function of the ambient temperature.The evaluation device preferably receives additional input signals, such as vehicle speed, tire pressure, and / or vehicle load, which allows for the consideration of (dynamic) tire stress (tire stress function, in particular a separate dynamic monitoring function) for the customer display. Dynamic tire stress is understood to be an influence that is more significant while driving than when the vehicle is stationary.

[0013] The drawing shows an embodiment of the invention. Fig. 1 schematically an example of the entirety of components of the tire inflation pressure control system according to the invention, Fig. 2 important components for creating a warning strategy according to the invention in the evaluation device, Fig. 3 an example of threshold values ​​for the air loss monitoring function and Fig. 4 an example of threshold values ​​for the load-bearing capacity monitoring function.

[0014] In Fig. Figure 1 is a tire pressure monitoring system consisting of an evaluation unit 1, an output unit 2 for issuing visual and / or audible warnings W1 and W2 to the driver, and the wheels LH, RH, LF, and RF of a vehicle, each equipped with a sensor unit. The sensor unit of wheel LH, for example, sends the measured tire pressure p_LH at the respective tire temperature T_LH to the evaluation unit 1. The respective current wheel-specific tire pressure values ​​p_LH, p_RH, p_LF, and p_RF at the respective current wheel-specific tire temperatures T_LH, T_RH, T_LF, and T_RF are collectively referred to as P(T) below. The evaluation unit 1 receives additional input signals from its own sensors or from sensors of other control units, in particular the vehicle speed v, the tire contact patch L, the vehicle load B, and, if applicable, the time t for time measurements between engine starts. Example implementation:

[0015] The customer sets a tire pressure P_init at a tire temperature T_init, given an ambient temperature TA_init. These values ​​are stored in the evaluation device 1, e.g., in the form of an evaluation unit of an electronic control unit. If the tire temperature T_init differs from TA_init at the time of initialization, the pressure P(T_init) is compensated according to the known formula up to an adjustable difference D_Tinit = T_init - TA_init. P_init(TA_init)=(P_init(Tinit)+P_Bar)*TA_init / T_init−P_Bar

[0016] Here, P_Bar is the barometric pressure and temperatures (TEMP) are to be considered in Kelvin. If the difference D_Tinit is greater than a certain maximum threshold, the initialization is rejected with a message indicating incorrect execution.

[0017] As in Fig. As shown in more detail in Figure 2, three separate monitoring functions are integrated into the evaluation device 1, for example, in the form of program modules 3, 4, and 5: the air loss monitoring function 5, the load-bearing capacity monitoring function 3, and the tire stress monitoring function 4. Based on these three monitoring functions 3, 4, and 5, the evaluation device 1 implements a new warning strategy. Based on the output signals of the three separate monitoring functions and according to a specific desired warning strategy, a prioritizer 6 issues the corresponding warning, here pre-warning W1 and main warning W2.

[0018] Based on Fig. Section 3 describes a possible warning strategy based on the air loss monitoring function 5: The initialized tire pressure P_init(TA_init) is compared with the current tire pressure P(T) in two different ways.

[0019] The current tire pressure P(T) is converted using the formula P(TA_init)=(P(T)+PBar)*TA_init / T - P_Bar and compared by comparing P(TA_init) and P_init(TA_init). Various thresholds are considered. One threshold, P_W2(TEMP), is mandated by law and requires an immediate main pressure loss warning W2, while a lower threshold, P_W1(TEMP), triggers a pre-warning W1. Additionally, the difference or percentage value of the pressure drop relative to P_init(TA_init) is preferably determined. This calculation triggers a warning W1 from the air loss monitoring function regarding the actual air molecule loss, or at least outputs it to prioritizer 6.

[0020] Based on Fig. Section 4 describes a possible warning strategy based on the load-bearing capacity monitoring function 3:

[0021] The current tire pressure P(T) is converted to the current ambient temperature TA using the formula P(TA) = (P(T) + P_Bar) * TA_init / T - P_Bar. This pressure is then compared to the initialization pressure P_init(TA_init), without taking temperature into account. Comparing the difference between P_init(TA_init) and P(TA) with a threshold, which can also be defined as a percentage of P_init(TA_init), triggers an early warning W1 from the load-carrying capacity monitoring function. Additionally, the percentage of the pressure decrease relative to P_init(TA_init) can also be determined. This analysis calculates the decrease in the tire's load-carrying capacity relative to the initialization pressure in a purely static comparison.

[0022] Additionally, the output of the tire stress monitoring function 4 can preferably also be included in the warning strategy: In addition to evaluating tire pressure by measuring and comparing pressures with thresholds according to various methods, the condition of the tire is determined in relation to the current driving situation (dynamically). Preferably, the vehicle speed v, the contact patch L and / or the load B are transmitted as input signals to the evaluation unit. From this, a tire stress value RB can be determined, which can be compared with a threshold value S_RB to, for example, identify a fundamentally critical situation (Situation 1, especially at high vehicle speed v) or to determine a generally non-critical situation (Situation 2, especially at low vehicle speed v).

[0023] In this embodiment, the tire stress monitoring function links four different detected situations to a value RB, which is then compared to a threshold S_RB. Additionally or alternatively, the tire stress monitoring function can output four different values ​​RB and / or situations without linking them to the prioritizer 6, whereupon the prioritizer 6 can itself perform linking functions.

[0024] Specifically, information such as driver classification, the current tire temperature T, the current difference between the ambient temperature TA and the tire air temperature T, the gradient of TA-T, the frequency of ambient temperature fluctuations (short-term fluctuations are not considered), and / or the tire-specific maximum speed can also be incorporated into the tire stress monitoring function. While methods for determining tire stress are generally known, according to the invention, this monitoring function is integrated into the new warning strategy, enabling separate monitoring functions to generate differentiated warning outputs, particularly pre-warnings.

[0025] The pre-warnings W1 of the individual monitoring functions 3, 4, and 5 can be the same or different. For simplicity, the example shown assumes only a single (identical) pre-warning W1. The timing of the pre-warning(s) W1 output to the output unit can be linked to situations such as the following, which can be stored and queried in a fill-possibility detection module 7: Regular reminders to check tire pressure In case the vehicle requires servicing For operating supplies; refilling of gasoline, oil, gas, windshield washer fluid, electrical energy requirements When the vehicle is detected to be entered (e.g., by changing the clamps after a prolonged period of inactivity), the tire temperature is not elevated compared to the ambient temperature. The driving situation is safe.

[0026] In a prioritizer (6), the available information is evaluated. A warning (W2) due to tire pressure loss must be displayed immediately upon reaching the legally prescribed threshold. Pre-warnings (W1), such as inflation instructions, are linked to specific situations that are relevant to the driver and service personnel.

[0027] The evaluation of additional information, such as load and driving behavior, may necessitate the immediate issuance of a pre-warning or a warning if the tire exhibits stress behavior. Temporary temperature fluctuations can delay the issuance of a pre-warning. Depending on the vehicle's display options, the driver receives additional information beyond the legally required indication of tire pressure loss and system failures. This information aims to clarify the situation and, together with instructions, ensure the warnings and warnings can be effectively resolved.

[0028] The warning strategy according to the invention makes it possible to control the warning based on the situation. A pre-warning, in the form of a notification, informs the driver in good time about the condition of the tire, thus preventing the risk of a breakdown. By taking driving characteristics and tire load into account, the actual tire condition can be warned about. The presented measure avoids, on the one hand, unnecessary tire pressure warnings, which can lead to customer complaints, and on the other hand, ensures tire condition monitoring that enables a warning regardless of the actual tire pressure and the associated monitoring capabilities. This allows the driver to monitor tire pressure and condition as effectively as possible. The driver's willingness to maintain their tires is thereby increased, making a positive contribution to CO2 reduction in accordance with legal requirements.

Claims

[1] Tire pressure monitoring system in a vehicle comprising at least one sensor for detecting the outside temperature (TA) and a sensor device on each wheel, which transmits at least the current tire pressure (P) and the current tire temperature (T) of the respective wheel to an evaluation device (1) permanently arranged in the vehicle, wherein the evaluation device (1) stores at least the respective tire pressure (P_init(T_init)) and the current outside temperature (TA_init) as initialization values ​​(INI) during an initialization process, detects their current values ​​(P(T), TA) during driving and, within the framework of an air loss monitoring function (5) and within the framework of a separate outside temperature-dependent load capacity monitoring function (3), causes the output of at least one pre-warning (W1) via an output unit (2),if the current tire pressure (P(TA)) converted to the current outside temperature (TA) falls below a predefined threshold (P_W1), whereby the decreasing load-bearing capacity of the tire with decreasing outside temperature (TA) is taken into account when defining the threshold, , characterized by , that the evaluation device (1) furthermore, within the framework of the air loss monitoring function (5), initiates an immediate pressure loss main warning (W2) via the output unit (2) when a predetermined threshold (P_W2(TEMP)) requires the immediate pressure loss main warning (W2). [2] Tire pressure monitoring system according to the preceding claim characterized by, that the evaluation device (1) by means of the outside temperature-dependent load-bearing capacity monitoring function (3) initiates a pre-warning (W1) when the difference between the current tire pressure (P(TA)) converted to the current outside temperature (TA) and the initialization pressure P_init(TA_init) exceeds a predetermined threshold (S_P3), whereby the decreasing load-bearing capacity of the tire with decreasing outside temperature (TA) is taken into account when defining the threshold. [3] Tire pressure monitoring system according to one of the preceding claims, characterized by , that the evaluation device (1) prevents an early warning (W1) to be initiated by the air loss monitoring function if no early warning (W1) is to be initiated yet due to the load-bearing capacity monitoring function. [4] Tire pressure monitoring system according to one of the preceding claims characterized by, that a further monitoring function is a separate tire stress monitoring function (4) in which the evaluation device (1) additionally receives at least one current tire condition variable (v, L, B) as an input signal and forms a tire stress value (RB) from it, and that the evaluation device (1) initiates a pre-warning (W1) when the tire stress value (RB) exceeds a predetermined threshold (S_RB) (Situation 1). [5] Tire pressure monitoring system according to the preceding claim characterized by , that the evaluation device (1) delays a pre-warning (W1) to be initiated by the air loss monitoring function (5) and / or by the load capacity monitoring function (3) until the tire stress value (RB) exceeds a predetermined threshold value (S_RB) (Situation 1). [6] Tire pressure monitoring system according to one of the preceding claims characterized by, that the load capacity monitoring function (3) is performed at a vehicle speed (v) below a specified speed threshold. [7] Tire pressure monitoring system according to one of the preceding claims characterized by , that the tire stress monitoring function (4) is performed at a vehicle speed (v) above a specified speed threshold.

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