DE102007007672B4 - Method for indirect tire pressure monitoring - Google Patents

Abstract

Method in which indirect tire pressure monitoring is carried out, with a tire pressure loss being detected and/or warned using two tire temperature variables (T _reset , T _akt ) determined separately in terms of time and/or at least one threshold value (S _akt ) which is Pressure loss detection is used based on an analysis of the movement of the wheels, depending on two tire temperature variables (T _Reset , T _akt ) determined at separate times, characterized in that the detection and/or warning of a tire pressure loss and/or the adjustment of the threshold value for Pressure loss detection (S _akt ) using a, in particular, specified, target tire pressure (p _Soll ) and a, in particular, specified, minimum tire pressure (p _Warn ) or using a, in particular specified, ratio of minimum tire pressure to target tire pressure (p _Warn /p _Soll ) is carried out .

Description

The invention relates to a method according to the preamble of claim 1. The invention also relates to a computer program product.

Systems that contribute to active or passive protection of the occupants are increasingly being used in modern motor vehicles. Tire pressure monitoring systems protect vehicle occupants from vehicle damage, which can be attributed to abnormal tire pressure, for example. Abnormal tire pressure can, for example, increase tire wear and fuel consumption or cause a tire defect ("burst tire"). Various tire pressure monitoring systems are already known, which either work on the basis of directly measuring sensors (directly measuring tire pressure monitoring systems) or detect abnormal tire pressure by evaluating speed or vibration properties of the vehicle wheels (indirectly measuring tire pressure monitoring systems).

From the DE 100 58 140 A1 An indirectly measuring tire pressure monitoring system (DDS: Deflation Detection System) is known, which detects a loss of tire pressure by evaluating the rotational movement of the wheel.

From the EP 0 578 826 B1 discloses a tire pressure determination device which determines a pressure loss in a tire on the basis of tire vibrations.

The DE 198 23 646 A1 discloses a method in which the temperature change is measured as a function of time and the temperature change is compared with a profile that is typical for the respective tire. If the measured time-dependent temperature curve exceeds the permissible one, a warning message is issued. Other factors such as vehicle movement and road conditions may also usefully be taken into account.

The DE 10 349 625 A1 discloses an outside temperature estimating device for estimating a temperature change outside a passenger compartment from a resonance frequency, which is a vibration component contained in a vehicle wheel speed signal, and a tire pressure detecting device for detecting a tire pneumatic pressure change in terms of the outside temperature change from the resonance frequency, which is contained in the vehicle wheel speed signal.

A method for evaluating a resonant frequency to detect whether the tire pressure of any wheel of the vehicle falls below a predetermined value is from the DE 103 31585 A 1 known. For this purpose, the resonant frequency of the wheel is recorded with a specified target pressure, the gradients of the frequency curve above and below are stored and their ratio is monitored.

From the DE 10 2005 004 910 A1 a method for indirect tire pressure monitoring is known with the following steps: - learning test variables that describe the wheel rotation of the wheels, - determining rolling circumference differences from currently determined test variables and the learned test variables, - learning at least one natural torsional frequency for at least one tire from the vibration behavior of the individual tires tires, - determining at least one shift in the torsional natural frequency from at least one currently determined torsional natural frequency and from the at least one taught-in torsional natural frequency, and - linking the differences in the rolling circumference with the at least one shift in the natural torsional frequency in a common warning strategy for detecting and warning of tire pressure loss.

The DE 697 14 140 T2 discloses techniques for estimating an air pressure condition of a tire of a motor vehicle based on movement of the vehicle wheel and the temperature of the tire.

The DE 10 2006 053 825 A1 relates to a method for indirect tire pressure monitoring, in which an analysis of the natural vibration behavior of at least one tire is carried out and a natural frequency is determined, with a temperature compensation of the pressure loss analysis variable being carried out, with a compensation variable, in particular the quotient of the change in the pressure loss analysis variable and the temperature change, being determined by means tire temperature calculated by a temperature model is used.

Indirectly measuring pressure loss detection methods usually include a learning phase and a pressure monitoring phase. In the learning phase, so-called comparative reference values are learned. In the pressure monitoring phase, which follows the learning phase, currently determined reference values are compared with the learned comparison reference values, taking into account threshold values for the pressure loss detection.

Furthermore, it is known that the temperature has an influence on the inner tire pressure. If, for example, the temperature of the air in the tire drops, the tire pressure also decreases. This temperature dependency must be taken into account for reliable tire pressure monitoring or tire pressure loss monitoring.

In the EP 0 895 880 A2 discloses an apparatus for estimating the air pressure of a tire, which includes a temperature sensor that measures the outside air temperature. The determined resonant frequency of the tire or the tire pressure estimated from it is corrected using the outside air temperature.

The object of the invention is to provide a method for indirect tire pressure monitoring that is suitable for improving an existing tire pressure monitoring system that measures indirectly or a combined tire pressure monitoring system that includes an indirect and a directly measuring tire pressure monitoring system.

According to the invention, this object is achieved by the method according to claim 1 .

The invention is based on the idea of detecting and/or warning of a loss of tire pressure and/or adjusting a threshold value for detecting pressure loss in an indirectly measuring tire pressure monitoring system using two tire temperature variables determined at different times. In contrast to the known tire pressure monitoring systems, in which a measured or determined tire pressure or a variable related to the tire pressure is corrected with regard to temperature, in the method according to the invention two tire temperature variables are used directly to adapt a pressure loss detection threshold value and/or to detect and/or warn of pressure loss . This makes it possible to identify an absolute minimum tire pressure.

According to the invention, the adjustment of the threshold value for detecting a pressure loss and/or the detection and/or warning of a tire pressure loss is carried out using a target tire pressure and/or a minimum tire pressure. Alternatively, the ratio of the minimum tire pressure to the target tire pressure can also be used for this. This makes it possible to determine a minimum temperature, which can be used to detect an absolute low pressure. Particularly preferably, the target tire pressure and/or the minimum tire pressure and/or the ratio of the minimum tire pressure to the target tire pressure is/are predetermined. The specified pressure(s) is/are very particularly preferably stored in a control unit in which the tire pressure monitoring algorithm is carried out. This eliminates the need for these values to be entered into the system, e.g. by the driver.

The two tire temperature variables determined separately in terms of time are preferably a tire temperature variable when a target tire pressure is set and a current tire temperature variable. As a result, the target pressure can be set by the driver at any desired temperature, and the change in temperature since the target tire pressure was set is taken into account.

The detection and/or warning of a loss of tire pressure is preferably carried out by comparing two tire temperature variables that are determined at different times. The direct comparison of the tire temperature variables eliminates the need for a time-consuming temperature correction of the variables associated with the tire pressure.

At least one tire temperature variable is advantageously learned when a means is actuated. In this context, it is particularly advantageous if the tire temperature variable is taught in when the target tire pressure is set when a means is actuated. The means, when actuated, the tire temperature variable is learned, is particularly preferably a switch or button. It is very particularly preferably a reset switch or button, which is also used to start a learning phase of the indirectly measuring pressure loss detection system.

According to a preferred embodiment of the method according to the invention, the tire temperature variable(s) is/are measured using at least one temperature sensor. A tire temperature sensor is particularly preferably used here.

It is also preferred to use the ambient temperature for the tire temperature variable(s). This is advantageous since the ambient temperature, e.g. determined by a sensor, is already present in most motor vehicles, and thus no additional costs are incurred for determining the tire temperature variables.

According to another preferred embodiment of the method according to the invention, the tire temperature variable(s) is/are calculated using a temperature model. This saves costs for temperature sensors. The driving profile and/or the tire load and/or environmental parameters are particularly preferably taken into account in the tire temperature model. The time profile of the vehicle speed and/or the ambient temperature and/or the vehicle standstill time are particularly preferably included in the model.

The method according to the invention is preferably carried out in an indirect tire pressure monitoring system, in which a pressure loss detection is carried out using a rolling circumference analysis of the tires and/or a frequency analysis of the natural vibration behavior of at least one tire. The method according to the invention can thus be used to improve such pressure loss detection systems which are known per se and carry out pressure loss detection using a rolling circumference analysis and/or a frequency analysis.

An advantage of the method according to the invention is that it is possible to detect and/or warn of an absolute minimum pressure in the tire. Furthermore, this detection and/or warning is independent of the external operating conditions of the vehicle or the tire(s). According to the method according to the invention, the setting of a target tire pressure advantageously no longer has to be carried out at a predetermined temperature.

The invention also relates to a computer program product which defines an algorithm according to the method described above.

Further preferred embodiments result from the subclaims and the following description based on figures.

• 1 ein schematisches Blockschaltbild eines beispielgemäßen Verfahrens zur indirekten Reifendrucküberwachung, und
• 2 schematisch Zusammenhänge zwischen einer aktuellen Reifentemperatur und einer Reifentemperatur bei Sollreifendruckeinstellung sowie die entsprechende Auswirkung auf die Anpassung eines Schwellenwerts zur Druckverlusterkennung.

Show it

• 1 a schematic block diagram of an exemplary method for indirect tire pressure monitoring, and
• 2 schematic relationships between a current tire temperature and a tire temperature at the target tire pressure setting and the corresponding effect on the adjustment of a threshold value for pressure loss detection.

As mentioned above, temperature has an impact on tire pressure. The operating instructions for a motor vehicle usually state that a specified tire pressure p _setpoint is to be set at a temperature of 20° C. and when the tires are cold (ie the ambient temperature corresponds to the tire temperature). In practice, however, this can hardly be ensured by the driver, and under certain circumstances he will also set the tire pressure at temperatures that deviate from the "target temperature". This is taken into account by the method according to the invention.

1 shows a schematic block diagram of an exemplary method for indirect tire pressure monitoring. In block 1, two tire temperature variables are determined at separate times, for example the tire temperature T _reset when the target tire pressure is set and the current tire temperature T _akt . These two tire temperature variables T _reset , _clock are evaluated and analyzed in block 2 together with a, for example, specified, desired tire pressure p _desired and a, for example, specified, minimum pressure p _warn to be warned. If a loss of tire pressure is detected, a warning is issued (block 3), for example to the driver of the vehicle. Alternatively or additionally, at least one threshold value S _akt for pressure loss detection is adjusted (block 4). If a pressure loss is detected based on the adjusted threshold value S _act , a warning is issued (block 3).

1. 1. Das System erhält die Information, dass der Solldruck des Reifens p_Soll anliegt. Dazu stellt der Fahrer den korrekten Druck p_Soll ein und gibt dies dem System, z.B. durch Betätigung eines Reset-Tasters, bekannt. Dies entspricht der Vorgehensweise in bekannten indirekten Systemen zur Reifendrucküberwachung.
2. 2. Bestimmung der effektiven Reifenlufttemperatur T_Reset, bei welcher der Reifendruck p_Soll eingestellt wurde. Hierfür kann z.B. ein Reifentemperatursensor eingesetzt werden oder der Messwert für die Umgebungstemperatur verwendet werden. Vorzugsweise berechnet man einen Näherungswert für die Reifentemperatur, der aus einem Reifentemperaturmodell ermittelt wird, welches auf Basis des Fahrprofils und der Reifenauslastung, im Wesentlichen mit den Eingangsgrößen Geschwindigkeiten, Standzeiten, Umgebungstemperatur etc., arbeitet.
3. 3. Mit Hilfe der Temperatur T_Reset und des dem System bekannten Solldrucks p_Soll für das Fahrzeug wird das Druck/Temperatur-Verhältnis c als Quotient aus Solldruck p_Soll und Temperatur T_Reset bestimmt: $$\text{c}={\text{p}}_{\text{Soll}}{\text{/T}}_{\text{Reset}}$$
   
4. 4. Bestimmung einer Mindesttemperatur T_Warn, bei der eine absolute Minderdruckwarnung auszugeben ist, aus dem zu bewarnenden Minderdruck p_Warn und dem Druck/Temperatur-Verhältnis c aus Gleichung (1) nach folgendem Zusammenhang: $${\text{T}}_{\text{Warn}}={\text{p}}_{\text{Warn}}\text{/c}$$
   
   Dieser Gleichung liegt physikalisch die Erkenntnis zugrunde, dass sich die Luft im Reifen wie ein ideales Gas verhält und das Reifenvolumen bzw. Gasvolumen V unveränderlich ist (d.h. das Verhältnis p durch T ist konstant).
5. 5. Ausgabe einer Minderdruckwarnung (Block 3) an den Fahrer, wenn der Reifen die Mindesttemperatur T_Warn aufweist oder darunter liegt, d.h. wenn die aktuelle Reifentemperatur T_akt kleiner oder gleich der Mindesttemperatur T_Warn ist: $${\text{T}}_{\text{akt}}\le {\text{T}}_{\text{Warn}},$$
   
   wobei die Mindesttemperatur T_Warn gemäß Gleichungen (1) und (2) durch den zu bewarnenden Minderdruck p_Warn, den Solldruck p_Soll und die Reifenlufttemperatur beim Reset T_Reset gegeben ist: $${\text{T}}_{\text{Warn}}={\text{p}}_{\text{Warn}}{\text{/p}}_{\text{Soll}}*{\text{T}}_{\text{Reset}}$$
   
6. 6. Optional kann eine Bestimmung des voraussichtlichen aktuellen Reifendrucks p_akt auf Basis der aktuellen Reifentemperatur T_akt, unter der Annahme, dass kein Luftmassenverlust stattfand, zu $${\text{p}}_{\text{akt}}=\text{c}*{\text{T}}_{\text{akt}}$$
   
   mit dem Druck/Temperatur-Verhältnis c nach Gleichung (1), durchgeführt werden.

An exemplary method for tire pressure monitoring, which can warn of an absolute minimum pressure p _Warn , is explained in more detail below (method steps 1 to 6). This is initially done under the assumption that the air mass in the tire does not change:

1. 1. The system receives the information that the target tire pressure p _target is present. To do this, the driver sets the correct pressure p _desired and informs the system of this, for example by pressing a reset button. This corresponds to the procedure in known indirect systems for tire pressure monitoring.
2. 2. Determination of the effective tire air temperature T _reset at which the tire pressure p _desired was set. A tire temperature sensor can be used for this, for example, or the measured value for the ambient temperature can be used. An approximate value for the tire temperature is preferably calculated, which is determined from a tire temperature model which works on the basis of the driving profile and the tire load, essentially with the input variables of speeds, idle times, ambient temperature, etc.
3. 3. With the help of the temperature T _reset and the target pressure p _target known to the system for the vehicle, the pressure/temperature ratio c is determined as the quotient of the target pressure p _target and the temperature T _reset : $$\text{c}={\text{p}}_{\text{Should}}{\text{/T}}_{\text{reset}}$$
   
4. 4. Determination of a minimum temperature T _Warn , at which an absolute low pressure warning is to be issued, from the low pressure p _Warn to be warned and the pressure/temperature ratio c from equation (1) according to the following relationship: $${\text{T}}_{\text{warning}}={\text{p}}_{\text{warning}}\text{/c}$$
   
   Physically, this equation is based on the knowledge that the air in the tire behaves like an ideal gas and the tire volume or gas volume V is unchangeable (ie the ratio p through T is constant).
5. 5. Output of a low-pressure warning (block 3) to the driver if the tire has the minimum temperature T _warn or is below it, i.e. if the current tire temperature T _akt is less than or equal to the minimum temperature T _warn : $${\text{T}}_{\text{act}}\le {\text{T}}_{\text{warning}},$$
   
   where the minimum temperature _Twarn according to equations (1) and (2) is given by the low pressure _pwarn to be warned, the target pressure _ptarget and the tire air temperature during reset _Treset : $${\text{T}}_{\text{warning}}={\text{p}}_{\text{warning}}{\text{/pp}}_{\text{Should}}*{\text{T}}_{\text{reset}}$$
   
6. 6. Optionally, the probable current tire pressure p _act can be determined on the basis of the current tire temperature T _act , assuming that there was no loss of air mass $${\text{p}}_{\text{act}}=\text{c}*{\text{T}}_{\text{act}}$$
   
   with the pressure/temperature ratio c according to equation (1).

The method described can therefore be carried out in a tire pressure monitoring system which has the following components or has access to the following information: target tire pressure p _target (e.g. specified), low pressure p _warning (e.g. specified), driver confirmation when target pressure p _target is set (e.g. by a reset button), ambient temperature or tire temperature or data on the tire load situation for improved prediction of the tire temperature (especially vehicle speed, vehicle idle time, moisture sensor if applicable).

Furthermore, the method according to the invention should be used in combination with known indirect systems for tire pressure monitoring, e.g. based on wheel speed information. The procedure is used here to adapt the warning thresholds of the indirect tire pressure monitoring system. In this case, air mass changes are also taken into account.

In a tire pressure monitoring system known per se, S ₂₀ is the warning threshold of the indirect tire pressure monitoring system for a pressure loss at a temperature of, for example, 20° C. (ie 293.15 Kelvin) and K is the criterion for a pressure loss, for example the difference between a taught comparison reference value and a current one Reference value that is linearly dependent on tire pressure. A pressure loss warning is issued by the method, which is known per se, if K is greater than the threshold S ₂₀ , ie K>S ₂₀ .

Zur Bewarnung eines absoluten Minderdrucks wird beispielsgemäß folgendermaßen vorgegangen:

1. a. Optional wird der aktuelle Reifendruck p_akt nach Gleichung (3), Punkt 6. des oben beschriebenen Verfahrens, berechnet.
2. b. Anpassung der Schwelle für eine Druckverlusterkennung S_akt mittels folgender Formel $$\begin{array}{l}{\text{S}}_{\text{akt}}={\text{S}}_{20}*\left({\text{T}}_{\text{akt}}{\text{/T}}_{\text{Reset}}*{\text{p}}_{\text{Soll}}-{\text{p}}_{\text{Warn}}\right)\text{/}\left({\text{p}}_{\text{Soll}}-{\text{p}}_{\text{Warn}}\right)\\ ={\text{S}}_{20}*\left({\text{T}}_{\text{akt}}-{\text{p}}_{\text{Warn}}{\text{/p}}_{\text{Soll}}*{\text{T}}_{\text{Reset}}\right)\text{/}\left({\text{T}}_{\text{Reset}}\right)\text{/}\left({\text{T}}_{\text{Reset}}*\left[1-{\text{p}}_{\text{Warn}}{\text{/p}}_{\text{Soll}}\right]\right),\end{array}$$
   
   in welche nur die aktuelle Reifentemperatur T_akt, die Reifentemperatur bei Sollreifendruckeinstellung T_Reset, der Reifensolldruck p_Soll und der zu bewarnende Minderdruck p_Warn eingehen.
3. c. Ausgabe einer absoluten Minderdruckwarnung, wenn das Kriterium K für einen Druckverlust die aktuelle, auf die Temperatur bezogene Schwelle S_akt überschritten hat: $$\text{K}>{\text{S}}_{\text{akt}}$$
   
   In analoger Weise kann natürlich auch das Kriterium K angepasst werden.

According to the invention, the threshold value(s) for pressure loss detection (block 4 in 1 ). A threshold S _act is functionally dependent on the current tire temperature T _act , the tire temperature at the target tire pressure setting T _reset , the target tire pressure p _target and the low pressure p _warn to be warned: $${\text{S}}_{\text{act}}=\text{f}\left({\text{T}}_{\text{act}},{\text{T}}_{\text{reset}},{\text{p}}_{\text{Should}},{\text{p}}_{\text{warning}}\right)$$

To warn of an absolute low pressure, the following procedure is used, for example:

1. a. Optionally, the current tire pressure p _act is calculated according to equation (3), item 6 of the method described above.
2. b. Adaptation of the threshold for a pressure loss detection S _act using the following formula $$\begin{array}{l}{\text{S}}_{\text{act}}={\text{S}}_{20}*\left({\text{T}}_{\text{act}}{\text{/T}}_{\text{reset}}*{\text{p}}_{\text{Should}}-{\text{p}}_{\text{warning}}\right)\text{/}\left({\text{p}}_{\text{Should}}-{\text{p}}_{\text{warning}}\right)\\ ={\text{S}}_{20}*\left({\text{T}}_{\text{act}}-{\text{p}}_{\text{warning}}{\text{/pp}}_{\text{Should}}*{\text{T}}_{\text{reset}}\right)\text{/}\left({\text{T}}_{\text{reset}}\right)\text{/}\left({\text{T}}_{\text{reset}}*\left[1-{\text{p}}_{\text{warning}}{\text{/pp}}_{\text{Should}}\right]\right),\end{array}$$
   
   into which only the current tire temperature T _akt , the tire temperature at the target tire pressure setting T _reset , the target tire pressure p _target and the reduced pressure p _warn to be warned are included.
3. c. Output of an absolute low-pressure warning if the criterion K for a pressure loss has exceeded the current temperature-related threshold S _act : $$\text{K}>{\text{S}}_{\text{act}}$$
   
   Of course, the criterion K can also be adjusted in an analogous manner.

In 2 an advantage of the method according to the invention is made clear, namely that a warning of an absolute minimum pressure p _Warn is possible. The ratio between target tire pressure p _target and warning pressure p _warn is usually fixed, for example p _warm /p _target =0.75. For this example, Equation (4) simplifies to: $${\text{S}}_{\text{act}}={\text{S}}_{20}*\left(4*{\text{T}}_{\text{act}}{\text{/T}}_{\text{reset}}-3\right)$$

In 1a the case is shown in which the current temperature T _act is below the temperature T _reset at which the reset was carried out and the setpoint pressure of the tire p _{setpoint was} present. Accordingly, the thresholds for the pressure loss detection are reduced, which is indicated by the arrows in 1a is indicated. Equation (4) also includes the borderline case in which the temperature T _akt has fallen so far that the current tire pressure p _akt corresponds to the tire pressure p _warn to be warned. In the example, this applies to T _act =3/4* T _reset , then the threshold value S _act becomes zero, as in 1c is shown.

In 1b the case is shown in which the current temperature T _act is greater than the temperature T _reset at reset. Accordingly, the thresholds for the pressure loss detection are increased, which is indicated by the double arrow in 1b is indicated. In both cases, the warning occurs at the same minimum pressure _pwarn .

A prerequisite for reliable and accurate pressure loss detection is, on the one hand, that the driver always sets the target pressure p _target exactly and then immediately carries out the reset. On the other hand, the criterion K for a pressure loss should depend linearly on the pressure. This is largely the case for the criteria that use known indirect tire pressure monitoring systems, such as changes in the rolling circumference or changes in the natural torsional frequency of the tire. A slight non-linearity can also be taken into account by appropriately adapting the formula from Equation (4).

An advantage of the method according to the invention is that the driver is allowed to set the target pressure at any temperatures. Another advantage is that, taking the temperature into account, a correct absolute low pressure can still be warned.

Claims (8)

Method in which indirect tire pressure monitoring is carried out, with a tire pressure loss being detected and/or warned using two tire temperature variables (T _reset , T _akt ) determined separately in terms of time and/or at least one threshold value (S _akt ) which is Pressure loss detection is used based on an analysis of the movement of the wheels, depending on two tire temperature variables (T _Reset , T _akt ) determined at separate times, characterized in that the detection and/or warning of a tire pressure loss and/or the adjustment of the threshold value for Pressure loss detection (S _akt ) using a, in particular, specified, target tire pressure (p _Soll ) and a, in particular, specified, minimum tire pressure (p _Warn ) or using a, in particular specified, ratio of minimum tire pressure to target tire pressure (p _Warn /p _Soll ) is carried out . procedure after claim 1 , characterized in that the two tire temperature variables determined separately in terms of time are a tire temperature variable when setting a desired tire pressure (T _reset ) and a current tire temperature variable (T _akt ). procedure after claim 1 or 2 , characterized in that at least one tire temperature variable, in particular the tire temperature variable when setting a target tire pressure (T _reset ), is taught when a means, in particular a switch or button, is actuated. Process according to at least one of Claims 1 until 3 , characterized in that the tire temperature values (T _reset , T _akt ) are measured by means of at least one temperature sensor, in particular a tire temperature sensor. Process according to at least one of Claims 1 until 4 , characterized in that the ambient temperature is used for the tire temperature parameters (T _reset , _clock ). Process according to at least one of Claims 1 until 5 , characterized in that the tire temperature values (T _reset , T _akt ) are calculated using a temperature model, in particular taking into account the driving profile and/or the tire load and/or environmental parameters and/or the vehicle idle time. Process according to at least one of Claims 1 until 6 , characterized in that in this a pressure loss detection based on a rolling circumference analysis of the tires and / or a frequency analysis of the natural vibration behavior of at least one tire is carried out. Computer program product for carrying out all steps of a method according to at least one of Claims 1 until 7 .

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