DE102007007672A1 - Method for indirectly monitoring tire pressure comprises recognizing and/or warning of a tire pressure loss based on separately determined tire temperature parameters and/or fitting a threshold value depending on the parameters - Google Patents

Abstract

Method for indirectly monitoring tire pressure comprises recognizing and/or warning of a tire pressure loss based on two separately determined tire temperature parameters and/or fitting a threshold value used for recognizing pressure loss based on an analysis of the movement of the wheels depending on the determined tire temperature parameters. An independent claim is also included for a computer program product for carrying out the above method. Preferred Features: The determined tire temperature parameters are a tire temperature parameter on adjusting a tire theoretical pressure and an actual tire temperature parameter.

Description

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

In modern motor vehicles are increasingly used systems, which contribute to the active or passive protection of the occupants. systems for tire pressure monitoring protect the vehicle occupants before vehicle damage, which, for example due to an abnormal tire air pressure. By an abnormal Tire pressure can For example, tire wear and fuel consumption increase or it can lead to a tire defect ("puncture") already different tire pressure monitoring systems known, which work either on the basis of direct measuring sensors (direct measuring tire pressure monitoring systems) or by evaluation of speed or vibration characteristics the vehicle wheels detect abnormal tire pressure (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 tire pressure loss by evaluating the wheel rotational movement.

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

Most of time include indirect pressure loss detection methods Training phase and a pressure monitoring phase. In the learning phase, so-called comparison reference values are learned. In the pressure monitoring phase, which follows the training phase are currently being determined Reference values under consideration of thresholds for the pressure loss detection with the learned comparison reference values compared.

Of Further, it is known that the temperature has an influence has the tire inflation pressure. If e.g. the temperature of the air in the tire decreases, so the tire pressure decreases. For reliable tire pressure monitoring or tire pressure loss monitoring must have this temperature dependence considered become.

In the EP 0 895 880 A2 For example, there is disclosed an apparatus for estimating the air pressure of a tire including a temperature sensor that measures the outside air temperature. In this case, the specific resonance frequency of the tire or the tire pressure estimated therefrom is corrected on the basis of the outside air temperature.

task The invention is a method for indirect tire pressure monitoring to provide, which for improvement of an existing indirect measuring tire pressure monitoring system or a combined tire pressure monitoring system which an indirect and a direct-measuring tire pressure monitoring system includes, is suitable.

These The object is achieved by the A method according to claim 1 solved.

Of the Invention is based on the idea, in an indirectly measuring Tire pressure monitoring system a detection and / or warning of tire pressure loss and / or an adjustment of a threshold value for pressure loss detection based two temporally separately determined tire temperature variables to perform. in the Contrary to the known tire pressure monitoring systems, in which a measured or determined tire pressure or a tire pressure related variable with respect to Temperature is corrected in the inventive method directly two tire temperature variables for Adaptation of a pressure loss detection threshold and / or to Pressure loss detection and / or warning used. This will a detection of an absolute minimum tire pressure possible.

According to one preferred embodiment of inventive method will adjust the threshold for pressure loss detection and / or the detection and / or warning of tire pressure loss below Use of a tire target pressure and / or a minimum tire pressure performed. alternative can do this also the relationship from minimum tire pressure to nominal tire pressure. hereby the determination of a minimum temperature is possible, which for detection an absolute reduced pressure can be used. Especially preferred is / are the nominal tire pressure and / or the minimum tire pressure and / or the relationship from minimum tire pressure to tire nominal pressure. Most notably Preferably, the predetermined pressure (s) are / are in one Controller, in which the tire pressure monitoring algorithm carried out is filed. This is eliminated the need for these values, e.g. by the driver, in the System must be entered.

The two temporally separated tire temperature values are preferably a tire temperature variable when setting a tire target pressure and a current tire temperature variable. Thereby For example, the desired pressure setting by the driver may be at any temperature and the change in temperature since the tire set point pressure is adjusted.

Prefers becomes the detection and / or warning of a tire pressure loss performed by comparing two, temporally separately determined tire temperature variables. By The direct comparison of the tire temperature variables eliminates a complex temperature correction the variables related to tire pressure.

advantageously, at least one tire temperature variable is taught in when an agent is actuated. It is particularly advantageous if the tire temperature size at setting the tire nominal pressure when actuated a device is taught. The means by which the Tire temperature size taught is particularly preferred is a switch or button. Most notably it is preferably a reset switch or button, which also for starting a training phase of indirectly measuring Pressure loss detection system is used.

According to one preferred embodiment of inventive method the tire temperature variable (s) is / are determined by means of at least one temperature sensor measured. Particularly preferred here is a tire temperature sensor for use.

As well it is preferable for the tire temperature size (s) the Ambient temperature to use. This is beneficial because in the Most motor vehicles have the ambient temperature, e.g. determined by a sensor already exists, and thus no additional costs for the determination of the tire temperature variables arise.

According to one another preferred embodiment of the method according to the invention is / are the tire temperature size (s) based on a Temperature model calculated. This will cost the temperature sensors saved. Particularly preferred are in the tire temperature model the driving profile and / or the tire load and / or environmental parameters considered. All the time profile of the vehicle speed is particularly preferred and / or the ambient temperature and / or the vehicle service life into the model.

The inventive method is preferably performed in an indirect tire pressure monitoring system, in which a pressure loss detection using a rolling circumference analysis the tire and / or a frequency analysis of the natural vibration behavior at least one tire is performed. The inventive method can thus, to improve such known pressure loss detection systems, which a pressure loss detection using a rolling circumference analysis and / or performing a frequency analysis.

One Advantage of the method according to the invention it is that detection and / or warning of an absolute minimum pressure in the tire possible becomes. Furthermore, this detection and / or warning is independent of the external conditions of use of the vehicle or tire (s). According to the method of the invention the setting of a tire target pressure must be advantageous no longer be carried out at a predetermined temperature.

The The invention also relates to a computer program product which has a Algorithm defined by the method described above.

Further preferred embodiments emerge from the dependent claims and the description below with reference to figures.

Show it

1 a schematic block diagram of an exemplary method for indirect tire pressure monitoring, and

2 schematically relationships between a current tire temperature and a tire temperature at nominal tire pressure setting and the corresponding effect on the adaptation of a threshold for pressure loss detection.

As already mentioned above, the temperature has an influence on the tire pressure. Usually in the operating manual of a motor vehicle that a predetermined tire pressure p _{target is set} at a temperature of 20 ° C and cold tires (ie the ambient temperature corresponds to the tire temperature). In practice, however, this is hardly ensured by the driver, and under certain circumstances he will also set the tire pressure at temperatures which deviate from the "setpoint 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, for example the tire temperature T _Reset when setting the desired tire pressure and the current tire temperature T _act , are determined separately over time. These two tire temperature variables T _Reset , T _akt are in block 2 together with a, eg predetermined, setpoint pressure of the tire p _setpoint and one, eg predetermined, to be warned minimum pressure p _Warn evaluated and analyzed. If a tire pressure loss is detected, a warning is issued (block 3), eg to the driver of the vehicle. Alternatively or additionally, an adaptation of at least one threshold value S _akt for pressure loss detection is carried out (block 4). If a pressure loss is detected on the basis of the adjusted threshold S _act , a warning is issued (block 3).

• 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. 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. 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 c = pSoll/TReset (1)
• 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: TWarn = PWarn/c (2)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. 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 Takt ≤ TWarn,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: TWarn = pWarn/pSoll·TReset
• 6. Optional kann eine Bestimmung des voraussichtlichen aktuellen Reifendrucks p_akt auf Basis der aktuellen Reifentemperatur Takt, unter der Annahme, dass kein Luftmassenverlust stattfand, zu pakt = c·Takt (3)mit dem Druck/Temperatur-Verhältnis c nach Gleichung (1), durchgeführt werden.

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

• 1. The system receives the information that the target pressure of the tire p _setpoint is present. For this purpose, the driver sets the correct pressure p _setpoint and makes this known to the system, eg by pressing a reset button. This corresponds to the procedure in known indirect systems for tire pressure monitoring.
• 2. Determination of the effective tire air temperature T _Reset , at which the tire pressure p _{setpoint has been} set. For this example, a tire temperature sensor can be used or the measured value for the ambient temperature can be used. Preferably, one calculates an approximate value for the tire temperature, which is determined from a tire temperature model, which operates on the basis of the driving profile and the tire load, essentially with the input variables speeds, service life, ambient temperature, etc.
• 3. With the help of the temperature T _Reset and the system known setpoint pressure p _setpoint for the vehicle, the pressure / temperature ratio c is determined as the quotient of setpoint pressure p _setpoint and temperature T _reset c = p Should / T reset (1)
• 4. Determination of a minimum temperature T _Warn at which an absolute reduced pressure warning is to be output, from the pressure to be warned p _Warn and the pressure / temperature ratio c from equation (1) according to the following relationship: T warning = P warning / c (2) 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 immutable (ie the ratio p through T is constant).
• 5. Output of a low pressure warning (block 3) to the driver when the tire is at or below the minimum temperature T _Warn , ie when the current tire temperature T _{act is} less than or equal to the minimum temperature T _Warn Cycle ≤ T warning . wherein the minimum temperature T _Warn according to equations (1) and (2) is given by the under pressure to be warned p _Warn , the target pressure p _Soll and the tire air temperature at the reset T _Reset : T warning = p warning / p Should * T reset
• 6. Optionally, a determination of the anticipated current tire pressure _{p.sub.actu may be} based on the current tire temperature, clock, assuming no air mass loss occurred p act = c · T act (3) with the pressure / temperature ratio c according to equation (1).

The method described can thus be carried out in a tire pressure monitoring system which has the following components or access to the following information: tire setpoint pressure p _setpoint (eg predetermined), reduced pressure p _warning (eg predetermined), driver confirmation at set target pressure p _setpoint (eg by a reset Button), ambient temperature or tire temperature or tire load situation data for improved tire temperature prediction (especially vehicle speed, vehicle life, possibly humidity sensor).

Farther should the inventive method in combination with known indirect tire pressure monitoring systems, e.g. based on wheel speed information, are used. in this connection the procedure is used to detect the warning thresholds of the indirect Adjust tire pressure monitoring system. In this case too Air mass changes considered.

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 eg 20 ° C (ie 293.15 Kelvin) and K the criterion for a pressure loss, eg the difference between a learned reference reference value and a current one Reference value, which depends linearly on the tire pressure. A pressure loss warning is issued by the per se known method if K is greater than the threshold S ₂₀ , ie K> S ₂₀ .

According to the invention, an adaptation of the threshold value es) to the pressure loss detection (block 4 in FIG 1 ). A threshold S _akt is in Functional dependency f of the current tire temperature T _act , the tire temperature at set tire pressure setting T _reset , the tire setpoint pressure p _setpoint and the lower pressure to be warned p _Warn adjusted: S act = f (t act , T reset , p Should , p warning )

• a. Optional wird der aktuelle Reifendruck p_akt nach Gleichung (3), Punkt 6. des oben beschriebenen Verfahrens, berechnet.
• b. Anpassung der Schwelle für eine Druckverlusterkennung S_akt mittels folgender Formel Sakt = S20·(Takt/TReset·pSoll – pWarn)/(pSoll – pWarn) = S20·(Takt – pWarn/pSoll·TReset)/(TReset·[1 – pWarn/pSoll]) (4), 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.
• c. Ausgabe einer absoluten Minderdruckwarnung, wenn das Kriterium K für einen Druckverlust die aktuelle, auf die Temperatur bezogene Schwelle S_akt überschritten hat: K > Sakt

To warn of an absolute reduction in pressure, the procedure is as follows, for example:

• a. Optionally, the current tire pressure p _{akt is} calculated according to equation (3), point 6 of the method described above.
• b. Adjustment of the threshold for a pressure loss detection S _act by means of the following formula S act = S 20 * (T act / T reset · p Should - p warning ) / (P Should - p warning ) = S 20 * (T act - p warning / p Should * T reset ) / (T reset · [1 - p warning / p Should ]) (4), in which only the current tire temperature T _act , the tire temperature at set tire pressure setting T _reset , the tire setpoint pressure p _setpoint and the lower pressure to be warned p _{Warn are received} .
• 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 : K> S act

In of course, of course also the criterion K be adapted.

In 2 an advantage of the method according to the invention is clarified, namely that a warning of an absolute minimum pressure p _{warning is} possible. Usually, the ratio between tire setpoint pressure p _setpoint and _warning pressure p _{warning is} fixed, eg p _Warn / p _setpoint = 0.75. For this example, equation (4) simplifies to: S act = S 20 · (4 · T act / T reset - 3)

In 1a the case is shown that the current temperature T _{act is} below the temperature T _Reset , at which the reset was carried out and the target pressure of the tire p _target was present. Accordingly, the pressure loss detection thresholds are reduced as indicated by the arrows in FIG 1a is indicated. Equation (4) also includes the limiting case that the temperature T _akt has dropped 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 _akt = 3/4 · T _Reset then the threshold S _akt becomes zero, as in 1c is shown.

In 1b the case is shown that the current temperature T _{akt is} greater than the temperature T _Reset at reset. Accordingly, the pressure loss detection thresholds are increased, as indicated by the double arrow in FIG 1b is indicated. In both cases, the warning is given at the same minimum pressure p _Warn .

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

One Advantage of the method according to the invention It is that the desired pressure setting to the driver at any Temperatures is allowed. Another advantage is that under consideration the temperature nevertheless warns of a correct absolute low pressure can be.

Claims (9)

Method in which an indirect tire pressure monitoring is performed, characterized in that a detection and / or warning of a tire pressure loss based on two temporally separately determined tire temperature variables (T _Reset , T _akt ) is performed and / or that at least one threshold (S _act ), which is used for pressure loss detection on the basis of an analysis of the movement of the wheels, is adjusted as a function of two temporally separately determined tire temperature variables (T _Reset , T _akt ). A method according to claim 1, characterized in that the detection and / or warning of a tire pressure loss and / or the adjustment of the threshold for pressure loss detection (S _act ) using a, in particular predetermined, nominal tire pressure (P _target ) and / or one, in particular predetermined, Minimum tire pressure (p _Warn ) or using a, in particular predetermined, ratio of minimum tire pressure to tire setpoint pressure (p _Warn / p _setpoint ) is performed. A method according to claim 1 or 2, characterized in that the two temporally separately determined tire temperature variables are a tire temperature variable when setting a tire setpoint pressure (T _Reset ) and a current tire temperature variable (T _act ). Method according to at least one of claims 1 to 3, characterized in that at least one tire temperature variable, in particular the Tire temperature variable when setting a tire setpoint pressure (T _Reset ), when a means, in particular a switch or pushbutton, is being taught-in. Method according to at least one of Claims 1 to 4, characterized in that the tire temperature variables (T _Reset , T _akt ) are measured by means of at least one temperature sensor, in particular a tire temperature sensor. Method according to at least one of claims 1 to 5, characterized in that the ambient temperature is used for the tire temperature variables (T _Reset , T _akt ). Method according to at least one of Claims 1 to 4, characterized in that the tire temperature variables (T _Reset , T _akt ) are calculated on the basis of a temperature model, in particular taking into account the driving profile and / or the tire load and / or environmental parameters and / or the vehicle service life , Method according to at least one of claims 1 to 7, characterized in that in this a pressure loss detection using a rolling circumference analysis of the tires and / or a frequency analysis the natural vibration behavior of at least one tire is performed. Computer program product for carrying out all Steps of a procedure according to at least one of the claims 1 to 8.