DE102005049442A1 - Tire pressure loss recognition system e.g. for motor vehicles, samples number of revolutions for each wheel, with which at constant vehicle speed dynamic rolling circumference is determined - Google Patents

Abstract

The system samples the number of revolutions for each wheel, with which at constant vehicle speed the dynamic rolling circumference is determined due to the measured revolutions and for a defined distance covered and compared to a stored reference value. The measurement of the revolutions for a defined actual distance covered (A) begins with the occurrence of a brief sound signal caused by roadway unevenness for a front wheel (Rvome) and ends with the occurrence of a brief sound signal caused by the same roadway unevenness on a rear wheel (Rhinten).

Description

The The invention relates to a system for detecting a tire pressure loss in motor vehicles according to the preamble of patent claim 1.

Such a system is, for example, in the unpublished DE 10 2004 029 370.8 described. Here, the time between two short-term changes in the wheel speed when driving over a road surface unevenness is considered first with the front wheel and then with the rear wheel to define the actual route.

Furthermore, the technical background on the DE 100 50 197 A1 pointed. In the DE 100 50 197 A1 the need for a change in the dynamic Abrollradius due to a pressure loss of changes in the dynamic Abrollradius is to be distinguished for performing a pressure loss detection with high accuracy, in particular by driving dynamics influences (such as cornering, potholes, acceleration) can be caused and in usually greater than the influence of a pressure loss on the dynamic rolling radius. The system known from it tries to recognize and hide the dynamic driving influences in a complex manner.

Known indirectly via The tire pressure monitoring systems that measure ABS sensors can either only be done by comparison Detect if a wheel pressure compared to the other wheels loses or they are based on a very elaborate and many confounders influenced verification of the tangential Radeigenfrequenz.

The Task, uniform in all wheels a vehicle running tire pressure losses, z. By natural diffusion the compressed air through the tire to the outside, to recognize, fulfill so far only very expensive, technically complex and against improper treatment very little robust telemetry systems.

Vehicle speed indicator (Tachometers) are ordinary calibrated to a single tire rolling circumference.

Indirectly Measuring tire pressure monitoring systems can only detect so far whether a tire compared to the other wheels on the vehicle clearly stronger Air loses ("flat tire"). Even in all four tire pressure losses can not be automatic be detected.

at Indirect measuring systems with tangential natural frequency measurement Different tires have a very different situation tangential eigenfrequency or are the resulting vibrations in the worst case on the vehicle does not pronounce sufficiently strong and can thus can not be detected.

Tacho ads Depending on the position of the rolling circumference of the attached tires, more or less inaccurate. To fulfillment the legal requirements for the speed indicator must the calibration values under certain circumstances be laid so that with individual tires significantly above the actual Speed values must be displayed, which is lead to customer complaints can. For vehicles for Rental companies are subject to the route law Gazette. The one for this permissible Tire rolling circumference tolerances are so small that for these Vehicles the spectrum more releasable Tire dimensions must be greatly reduced.

task The invention is by means of inexpensive software without additional Hardware installation in vehicles already equipped with ABS sprockets and ABS sensors (eg cars, motorbikes, Quads) in all wheels substantially uniform tire pressure losses early enough and sure to recognize.

These The object is achieved by a Method according to claim 1 solved. Advantageous developments are the objects the dependent Claims.

Of the The invention is based in particular on the knowledge that a pressure loss in the tire is easy to determine if it is known how many times a wheel at a given actual Has turned the route. The problem here is the assignment to a given actual Route. Because the speedometer signal is very inaccurate, because this is usually also about the Wheel speed sensors can be determined from the speedometer speed signal no actual Driving distance can be specified. Basis of the invention is a exact information about a real traveled To get driving distance. Because thus can only over the Wheel speed of a wheel based on the actual distance traveled absolute pressure loss can be detected. With a very accurate working navigation system could For example, associated with such a given actual driving distance become.

In particular, according to the invention an actual route through a time window between given two detectable events that mark the beginning and end of the actual route. If, for example, the distance between two posts detectable via camera sensors would be known, this distance could be specified as the actual route. According to the invention, the wheel speed for each wheel is determined precisely between the times at which the events occur and are detected. From the wheel speed of each wheel measured in this time window, the pressure loss becomes absolutely detectable by known calculation of the respectively associated dynamic rolling circumference or rolling radius.

When Especially advantageous has been calibrated as actual Distance of the wheelbase exposed, the invention by a time window between two events is given, the beginning and mark the end of a route that is just as long as the Wheelbase is. The events for this invention are the short-term Speed changes first on the front wheel and then on the rear wheel due to a Roadway unevenness.

Instead of the short-term speed changes first on the front wheel and then on the rear wheel can also be a short-term Sound event first from the front wheel and then from the rear wheel due to overrunning a road surface roughness the beginning and the end of the time window Show.

at Vehicles with voice recognition and / or hands-free telephone equipment is already on Microphone on board, which for the recording of low-frequency characteristic sound events when driving over can be used by road bumps.

The Microphone signals are preferably transmitted via a suitable low-pass filtering according to the Sound characteristic when driving over of road bumps filtered out from other sound events become.

In the drawing is an embodiment of Invention shown. The single figure shows that for the invention essential recognition of a defined actual route by in-vehicle means.

A vehicle F (drawn by a solid line) passes over z. B. with its right front wheel R _front (or with two front wheels) at time t _front a road surface unevenness FU. After the defined actual distance A in the form of the wheelbase, at least the right rear wheel R _at the _{rear of} the vehicle F (now marked with a dashed line) _{travels over the} same road surface unevenness FU _at the time t. The occurrence of the road surface unevenness FU on the front wheel R _front causes a momentary change in the wheel speed n _front or generates a short low-frequency sound event. The occurrence of the road unevenness FU at the rear wheel R _behind (the same vehicle side) causes a short-term change in the wheel speed n _behind or again generates a short low-frequency sound event. The changes of the wheel speeds n n _{behind the front} are indicated in the drawing by small signal dips in the illustrated schematically otherwise substantially constant speed gradients. The speed curves are substantially constant, since the invention presupposes the presence of the condition of a constant vehicle speed v.

Analogous the signal collapses would be at Application of the sound method in place of small signal dips one short-term increase of the sound signal level use.

In the following, the operation of the system according to the invention will be explained in more detail in a particularly advantageous embodiment:
The system according to the invention is advantageously integrated in an electronic control unit for brake systems, which already receives the input signals of very accurate wheel speed sensors in a known manner. The wheel speeds of each wheel are detected via one ABS speed sensor per wheel position (ie in a four-wheeled motor vehicle: front left wheel, front right wheel, rear left wheel and rear right wheel). The wheel speed sensors usually detect the teeth or tooth flanks of a sensor disc provided with, for example, 48 teeth, which is non-rotatably connected to each wheel and co-rotates.

When driving at a constant speed v, the speed n _{i of} each wheel (with i = 1, 2, 3, 4, the numbers 1 to 4 denote the four wheel positions: eg 1 for front left, 2 for rear left, 3 for front right , 4 for the rear right), although individually slightly different, but temporally in principle as long as constant, as well as the driving speed v is constant.

The wheel speed n is calculated from n = v / U _dyn , where U _{dyn is} the dynamic rolling circumference of the tire under the specific driving conditions (wheel load, speed, tire pressure, type of tire, etc.).

If a tire drives over a road surface irregularity or an obstacle (eg road cross gap, pothole), the wheel speed changes briefly during the passage of the obstacle, because each obstacle crossing with a short-term loka len change the tire compression travel and thus the tire rolling circumference is connected.

With exact determination of the time intervals t _i (with i = 1 ... 96, corresponds to 96 flanks with 48 teeth or with i = 1 ... 48, corresponds to 48 teeth), in which z. B. passing two successive teeth or tooth flanks on the ABS speed sensor, it can be stated that these time intervals during the passage of the tire over an obstacle briefly compared to - calculated over a whole Radumdrehung - average t _transverse (t _transverse = time t for change a wheel revolution / Z _{constructively.} In this case, Z is _structurally the structurally predetermined number of teeth (for example 48) or tooth flank number (eg 96) of the ABS-toothed rims.

A simple method for detecting an obstacle-crossing would be a threshold for the difference t _ts - t _i define in its magnitude exceeding one obstacle-crossing with reasonable certainty can be postulated. The threshold must be determined vehicle-specific by tests.

at driving forward will be an obstacle on each side of the vehicle first from the front wheel and only then run over by the rear wheel of the same vehicle side. As a result, it is appropriate, this Obstacle detection first with a front wheel of the respective vehicle side perform and then with the rear wheel of the same vehicle side.

As soon as such a change in the time interval on a front wheel is sufficiently clearly detected, it is provided with the time stamp (time point) t _front . Simultaneously with the time t _front z. B. for each wheel position started its own counter, which counts up from the time t _front ABS sensor tooth or tooth edge pulses z1, z2, z3 and z4 each wheel. The numbers 1 to 4 again denote the four wheel positions; eg 1 for front left, 2 for rear left, 3 for front right, 4 for rear right. The count z _i is therefore synonymous with a speed n _i for each wheel.

An obstacle crossing detected at the front wheel at the time t _{at the front is also} detected _{at the rear} by the rear wheel at a later time t when the obstacle detection described above is applied there in the same way.

At the time t _back , according to the embodiment, the counter started _at the time t is stopped. This corresponds to the general statement according to the invention that the measurement of the wheel speed for a defined actual distance A in the form of the wheelbase when a short time caused by a road surface unevenness change of the wheel speed n _{front of} at least one front wheel on a vehicle side starts and when a brief by same road surface roughness caused change in wheel speed n _behind at least the rear wheel ends on the same side of the vehicle.

The counter readings are then Z1, Z2, Z3 and Z4 and always belong to the same time interval t _behind - t in _front .

Once t _front and t _{back are} determined, from the wheelbase A of the vehicle (= distance between the wheel centers of front and rear axle), the constructive predetermined tooth or tooth flank number Z _{constructive of} the ABS sensor sprockets and the respective meter readings Z1, Z2 , Z3, Z4 calculate the tire rolling circumferences R _dyn1 , R _dyn2 , R _dyn3 or R _dyn4 that are individually different at each wheel _position according to the following formula: R dyni = (Z constructive × A) / (Z i × 2 × π) (where i = 1, 2, 3 or 4)

It is known from the development of so-called "indirectly measuring tire puncture warning systems" that a tire reduces its dynamic rolling circumference or rolling radius R _dyn in the event of pressure loss. If the dynamic rolling circumference or rolling radius of a tire is determined immediately after setting the tire pressure according to the above-mentioned method and if this value is stored as the starting value or reference value in the control unit, upon further observation of the dynamic rolling circumference or rolling radius according to the above method be diffusion-related pressure loss through reduction of R _dyn - detected value. If a certain limit value is undershot, a message to the driver can be triggered.

• – Es werden nur diejenigen Zeitintervalle t_hinten – t_vorne betrachtet, in denen nur eine einzige Hindernisüberfahrt detektiert wird.
• – Es werden nur diejenigen Zeitintervalle t_hinten – t_vorne betrachtet, in denen die zeitliche Abfolge kurz aufeinanderfolgender Hindernisse gleich ist.
• – Eine Meldung an den Fahrer wird nur ausgelöst, wenn die R_dyn – Reduktion in einer zu definierenden Anzahl lückenlos aufeinander folgender Detektionsfälle festgestellt wurde.
• – Eine Meldung an den Fahrer wird nur ausgelöst, wenn die R_dyn – Reduktion bis zu einer zu definierenden Summe kumulierter Detektionsfälle festgestellt wurde.
• – Der Detektionsalgorithmus wird abgebrochen, sobald die aus der Zeitdifferenz t_hinten – t_vorne und dem Radstand A errechenbare mittlere Fahrgeschwindigkeit V_mittel = A/(t_hinten – t_vorne) sich um mehr als einen zu definierenden bestimmten Betrag von der über das Tachosignal ermittelten Fahrgeschwindigkeit v_Tacho unterschreitet.

Since road unevenness or obstacles in distance and altitude are usually stochastically distributed according to experience, the above-mentioned calculation values must be determined several times and checked for statistical relevance. This can be done with different methods. Some of them are described by way of example and may be used either alone or in combination with each other.

• - Only those time intervals t _behind - t _are considered in _front , in which only a single obstacle crossing is detected.
• - Only those time intervals t _behind - t _are considered in _front , in which the chronological sequence of short consecutive obstacles is the same.
• A message to the driver is only triggered if the R _dyn reduction has been determined in a number of completely consecutive detection cases to be defined.
• - A message to the driver is only triggered if the R _dyn reduction was detected up to a sum of accumulated detection cases to be defined.
• The detection algorithm is aborted as soon as the mean vehicle speed V _average = A / (t _rear - _front ) calculated from the time difference t _rear -t _front and wheelbase A is more than one specific amount to be defined from that determined via the tacho signal Driving speed v _{Tacho falls} below.

Conversely, from the last consideration, the correctness of the tacho signal v _{Tacho can be} verified. This is particularly helpful when the previously common standard tacho calibration must be abandoned because the range of rolling circumferences of tires that can be used on the vehicle is so great that the legally permissible tolerances can no longer be met with a single calibration number.

In addition will pointed out that the here to be determined tire pressure loss occurs very slowly and for detection or notification to the driver sufficient time in the order of magnitude of weeks, in which an evaluation of the measurement results is possible.

The The functions described above can also be applied mutatis mutandis to motorcycles provided they are on both wheels with corresponding sprockets (e.g., as well as for ABS used) are equipped.

With The method described, it is cheaper by means of Software possible, without additional Hardware installation in vehicles already equipped with ABS sprockets and sensors (cars, Motorcycles, Quads) in all wheels uniform or nearly even tire pressure losses early enough indicating a significant drop in tire life and the tire properties is intercepted. Have this ability so far only very expensive telemetry tire pressure monitoring systems. The described detection functions are simple constructive Vehicle dimensions (wheelbase, ABS sprocket) adjustable and not from relatively difficult to detect and unstable tire natural frequency analyzes dependent.

As well the tachometer is automatically specified in a very simple way and the usual tire influence bypassed.

Claims (1)

System for detecting a tire pressure loss in motor vehicles while driving with means for detecting the wheel speed of each wheel, in which at constant vehicle speed for each individual wheel, a variable proportional to the dynamic rolling circumference due to the measured for a defined actual distance wheel speed of each wheel is determined which is compared with a stored reference value, characterized in that the measurement of the wheel speed for a defined actual distance (A) in the form of the wheelbase when a short time caused by a road surface unevenness sound signal at least one front wheel starts and at the occurrence of a brief by the same Road surface roughness caused sound signal at least one rear wheel ends.