Method and system for the detection of a pressure drop in a tire

A system for the detection of a pressure drop in a tire comprising a tire air pressure sensor, a tire temperature sensor and an evaluating unit. The evaluating unit converts the measured air pressure values and temperature values into temperature compensated air pressure values and produces an alarm signal when the temporal fluctuation exceeds an air pressure fluctuation threshold value. The evaluating unit decreases the air pressure threshold value with increasing deviation from the measured temperature compensated air pressure value of a predetermined temperature compensated air pressure reference value. At least one further sensor may be provided for measuring a parameter which influences the air pressure in the tire whereby the evaluating unit corrects the measured and, regarding to the production of an alarm signal, evaluated air pressure according to this parameter.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority German Application number 101 44 361.7, filed Sep. 10, 2001, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The present invention relates to the detection of pressure drop in a tire and more particularly to a method and a system for the detection of a pressure drop in a tire and for generating an alarm after a certain drop in pressure has occurred. The invention is suitable for the detection of a pressure drop in all types of pneumatic tires. It is especially suitable for vehicle tires, like passenger car tires, truck tires, motorcycle tires, etc.

A vehicle tire monitoring system is set out in U.S. Pat. No. 5,895,846, wherein the system: periodically measures the air pressure and temperature in the tire; corrects the measured temperature; and creates an alarm signal if the temperature corrected air pressure changes over time by more than a threshold amount.

SUMMARY OF THE INVENTION

The invention is based upon a task of finding a method to more precisely note an undesired pressure drop in a tire that might result in the tire becoming unroadworthy. A first solution to this objective is obtained as follows. The air pressure fluctuation threshold value depends on the momentary measured air pressure and it is possible to reduce the air pressure fluctuation threshold value preferably with decreasing measured temperature compensated air pressure so that the instant method works more sensitively. Another solution to the invention's task is obtained whereby the measured air pressure is not compensated only with regard to the measured temperature, but also with regard to at least one additional parameter influencing the air pressure in the tire, for example the external air pressure or the velocity of a vehicle. Yet another solution of the invention's task is obtained from implementation which is particularly safe and free of external influences because air pressure fluctuations are detected and evaluated over a lengthy period of time.

Other solutions are provided by the present invention which comprises a method for detecting an air pressure drop in a tire, comprising the steps of: measuring air pressure within said tire; measuring air temperature within said tire; converting measured air pressure into a temperature compensated second air pressure, said converting being in accordance with said measured temperature; determining temporal fluctuations of said temperature compensated second air pressure, said fluctuations being in accordance with a difference between said temperature compensated second air pressure and a predetermined temperature compensated reference air pressure; and generating an alarm if said fluctuations exceed a predetermined threshold.

Still other solutions are provided by the present invention which comprises a method for detecting a pressure drop in a tire, comprising the steps of: measuring air pressure within said tire; measuring air temperature within said tire; converting said air pressure into a temperature compensated air pressure corresponding to said temperature; determining temporal fluctuation of said temperature compensated air pressure; generating an alarm signal when said temporal fluctuation of said temperature compensated air pressure exceeds an air pressure threshold value, wherein at least one additional parameter which influences air pressure in said tire is measured; and updating determined temporal fluctuation of said temperature compensated air pressure according to said measured additional parameter.

Still other solutions are provided by the present invention which comprises a method for detecting air pressure drop in a tire, comprising the steps of: measuring air pressure with said tire; measuring air temperature within said tire; converting said air pressure into a temperature compensated air pressure corresponding to said temperature; determining temporal fluctuation of said temperature compensated air pressure; generating an alarm signal when said air pressure fluctuates in a predetermined way wherein: deviations of at least two consecutively measured temperature compensated air pressure values are stored together with respective times when respective deviations exceed a predetermined first threshold value; a sum of the stored deviations within a predetermined time interval is calculated; and said alarm signal is generated when said sum exceeds a predetermined second threshold value.

Still other solutions are provided by the present invention which comprises a system for detecting air pressure drop in a tire, comprising: an air pressure sensor for detecting air pressure in said tire; a temperature sensor for detecting air temperature in said tire; an alarm generator for generating a human detectable alarm; and an evaluating unit connected to said air pressure sensor, temperature sensor, and alarm generator; said unit comprising: means for evaluating signals from said air pressure and temperature sensors, means for converting measured air pressure values and temperature values into temperature compensated air pressure values, means for determining temporal fluctuations of said compensated air pressure values, means for causing an alarm to generate at said alarm generator when said temporal fluctuation exceeds an air pressure fluctuation threshold value, and means for decreasing said air pressure fluctuation threshold value with increasing deviation of said measured temperature compensated air pressure value by a predetermined temperature compensated air pressure reference value.

Still other solutions are provided by the present invention which comprises a system for detecting air pressure drop in a tire, comprising: an air pressure sensor for detecting air pressure in said tire; a temperature sensor for detecting air temperature in said tire; at least one additional sensor for measuring a parameter which influences air pressure in said tire; an alarm generator for generating a human detectable alarm; and an evaluating unit in electrical communication with said air pressure sensor, temperature sensor, at least one additional sensor, and alarm generator, said unit comprising means for: converting measured air pressure values and temperature values into temperature compensated air pressure values, determining temporal fluctuation of said compensated air pressure values, causing alarm signals to be generated in said alarm generator when said temporal fluctuation exceeds a threshold value, and correcting said temporal fluctuation in accordance with said parameter.

Still other solutions are provided by the present invention which comprises a system for the detection of a pressure drop in a tire, comprising: an air pressure sensor for detecting air pressure in said tire; a temperature sensor for detecting temperature in said tire; an alarm generator for generating a human detectable alarm; and an evaluating unit in electrical communication with said air pressure sensor, said temperature sensor, and alerting unit, said unit comprising means for: converting measured air pressure values and temperature values into temperature compensated air pressure values and producing an alarm signal when said temperature compensated air pressure fluctuates in a predetermined way; storing deviations of two temperature compensated air pressure values measured in predetermined time intervals together with associated times thereof; and when a deviation exceeds a predetermined first threshold value, further calculating a sum of stored deviations of a time interval whose length is predetermined and producing an alarm signal at said alarm generator when said sum exceeds a predetermined second threshold value.

DETAILED DESCRIPTION OF THE INVENTION

As shown inFIG. 1, a pressure sensor4for the detection of air pressure inside a tire, and a temperature sensor6for the detection of temperature inside the tire, are placed in vehicle tire2. Structure and function of such sensors are known to one skilled in the art. Pressure sensor4does not necessarily have to be placed immediately within the interior space of the tire. Rather, it can also be placed at a valve, such that the pressure sensitive element of pressure sensor4detects the internal pressure of the tire. The temperature detected by temperature sensor6should be little influenced by the wall of the tire, so that the temperature sensor can be placed, thermally insulated, at the rim. If the pressure sensor4is placed at the valve and the temperature sensor6is not placed at the internal wall of the tire, but at the rim, the tire itself is not affected by the sensors. It is also possible to install both sensors at the valve or at the rim.

The output signals of sensors4and6are transmitted to an evaluating unit8. Depending upon the structure and arrangement of the sensors, this may occur as follows: mechanically by sliding contact; wirelessly in generally known ways such as inductively, capacitively, unidirectionally by radio, or bidirectionally by transponders which communicate with a sending/receiving unit10which further edits the signals sent from the assigned transponders by the sensors and supplies input to evaluating unit8. An ambient air pressure sensor12and a velocity sensor14are connected to the inputs of the evaluating unit8as well.

The evaluating unit8comprises a generally known microprocessor16with a program memory18and a data memory20. An output of evaluating unit8is directed to monitoring, alarm, or alerting unit22which may comprise a warning light or a display in a vehicle dashboard along with acoustic output if desired. A first method embodiment of the present invention is set out with reference to the flow chart of FIG.2.

The method starts in step30and proceeds to step32wherein pressure and temperature values of a predetermined cycle of sensors are stored into memory of evaluating unit8. The stored values are edited in step34, for example filtered, to eliminate transient fluctuations or external interferences. In step36, the processed and read pressure values will be compensated with the processed and read temperature values according to the example formula pc=pm×Tc/Tm, wherein pcis the temperature compensated and measured pressure value, pmis the measured pressure value, Tc is a reference temperature, and Tm is the measured temperature. The temperatures are in absolute temperature values. The temporal fluctuation of the pressure values generated and compensated in step36are then calculated in step38wherein various methods may be used, including: a successive communication over n values; or only the fluctuation of each of two values measured in constant consecutive intervals. It is determined in step40if the temporal fluctuation of the measured compensated pressure values determined in step38lies above an air pressure fluctuation threshold value of ps. If this is not the case, the method returns to step32. If this is the case, an alarm signal is produced in step42.

According to another embodiment of the present inventive method, the air pressure changed threshold psis not a constant predetermined value, but dependent upon the difference between a prestored temperature compensated pressure value—which is for instance the optimal temperature compensated tire air pressure—and the currently measured compensated pressure value pswhich is continuously calculated in the evaluating unit and becomes smaller with increasing deviation so that the system increasingly reacts more sensitively in increasingly dangerous situations during which the air pressure increasingly drops.

The air pressure fluctuation threshold value psis a constant, predetermined, stored value, in another embodiment of the invention, and the pressure values are not only compensated dependant upon the measured temperature in step36, but dependant on further parameters influencing the internal pressure of the tires, like the measured ambient air pressure by the sensor12and/or the measured vehicle velocity by velocity sensor14. The compensation then occurs according to the general formula:

pc=pm×f(T, xi), wherein f(T, xi) is a function which indicates an independent value of the conversion of the measured pressure value, parameter T influences the temperature, and parameters xiinfluence the pressure. The compensation can alternatively or additionally occur for the threshold value fluctuation.

The inventive systems and methods can be modified in various respects. For example, the time of the temporal pressure fluctuation, determined in step40, can be extrapolated for when a predetermined low and dangerous air pressure will occur, so that the driver of a vehicle can assess how long he can still drive on a tire with an effected pressure drop. Further, the above mentioned reference air pressure, which corresponds to an optimal tire air pressure, can not only be compensated corresponding to temperature, but also other factors which influence the optimal air pressure, like the vehicle's load, the vehicle's velocity, etc. Likewise, a stored and improperly low air pressure level, the undermining of which will generate a warning signal and exceeding of which will be calculated where appropriate, can depend upon such parameters.

FIG. 3depicts a flowchart, based uponFIG. 2, comprising another embodiment of the present invention. The steps30to36coincide with the same numbered steps in FIG.2. In step50, the difference between the current and a previously determined measured or compensated pressure value Δpis calculated. If this is the case, the deviation Δpis then stored in step54together with the time of its determination. The sum of the deviations Δpiwhich have occurred within a predetermined time interval, is determined in step56. If it has been determined, in step52, that Δpis less than or equal to the predetermined first threshold value ps1, then the system jumps immediately to step56. It is determined in step58if the generated sum in step56is greater than the second threshold value pS2. If this is not the case, the system then jumps back to step32. If this is the case, an alarm signal is then generated in step60.

An advantage which is achieved with the method according toFIG. 3lies therein that within each determined sum generation in step56and a time interval which is predetermined in its length, only those pressure deviations are detected which are above the threshold according to step52. Subtle pressure deviations which are for example only conditioned by fluctuations of the ambient pressure or other such parameters are suppressed from the start. It is understood that the threshold values of the steps52and58, as well as the time interval of step56, can be adjusted to certain conditions, such as to the determined compensated pressure value, ambient temperature, vehicle velocity, vehicle load, etc.