DE102004029370A1 - System for detecting a tire pressure loss in motor vehicles - Google Patents

Abstract

In a system for detecting a tire pressure loss in motor vehicles while driving with means for detecting the wheel speed of each wheel at constant vehicle speed for each wheel a proportional to the dynamic rolling circumference size is determined based on the measured for a defined actual distance wheel speed of each wheel, the is compared with a stored reference value.

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 from the DE 100 50 197 A1 known. In the known document, the need is addressed that to perform a pressure loss detection with high accuracy, a change in the dynamic Abrollradius due to a pressure loss of changes in the dynamic Abrollradius is to be distinguished, in particular by driving dynamics influences (such as cornering, potholes, acceleration) are caused and which are usually larger than the influence of a pressure drop 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 measuring ABS sensors can only detect by comparison operations, whether one wheel loses pressure compared to the other wheels or they are based on a very elaborate and of many confounding factors 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 The odometer is subject to the calibration law. The permissible tire rolling circumference tolerances are so small that for these vehicles greatly increase the spectrum of releasable tire dimensions must be 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, motorcycles, Quads, trucks possibly also with trailer, if this also with ABS sensors equipped is) 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 driving route is predetermined by a time window between two detectable events which characterize the beginning and the end of the actual driving route. If, for example, the distance between two posts detectable via camera sensors could be known as the actual driving distance this distance can be specified. 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.

The inventive system also includes the application in cars or trucks with trailer, provided the trailer Has ABS sensors whose signals are routed to the control unit in the vehicle become. In a uniaxial trailer must also in the control unit Distance of trailer wheels from one of the axles of the (towing) vehicle as (second) wheelbase with be stored corresponding to the corresponding wheels. at a biaxial trailer must be in the control unit the wheelbase of these two axles as (second) wheelbase with corresponding Related to the associated wheels be stored.

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 short-term change in the wheel speed n _front . The occurrence of the road surface unevenness FU on the rear wheel R _{at the rear} (same side of the vehicle) causes a short-term change in the wheel speed n _behind . The changes in the wheel speeds n _back and n _front are indicated in the drawing by small signal dips in the otherwise shown otherwise substantially constant speed curves. The speed curves are substantially constant, since the invention presupposes the presence of the condition of a constant vehicle speed v.

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 one with for example 48 teeth provided encoder disc, which is rotatably connected to each wheel and co-rotated.

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.).

Drive in Mature over a roadway bump or obstacle (e.g., roadway joint, pothole), so changes while the crossing of the Obstacle briefly the wheel speed, because every obstacle crossing with a brief local change in the tire deflection path and connected to the tire rolling circumference.

With exact determination of the time intervals t _i (with i = 1 ... 96, corresponds to 96 edges with 48 teeth or with i = 1 ... 48, corresponds to 48 teeth), in which eg two consecutive teeth or tooth flanks on the ABS speed sensor passing by, it can be seen that these time intervals during the passage of the tire over an obstacle for a short time compared with the calculated over a whole Radumdrehung average t _transverse (t _transverse = time t for a Radumdrehung / Z _{constructively} change Z is _constructive constructively specified number of teeth (eg 48) or number of tooth flanks (eg 96) of the ABS sprockets.

A simple method for detecting an obstacle crossing would then be to define a threshold value for the difference t _cross -t _i in whose amount exceeding an obstacle crossing is to be postulated with sufficient probability. 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 unevenness 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 _back -t _forward .

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 dyn i = 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 detected diffusion-related pressure loss by decreasing the R _dyn value. If a certain limit value is undershot, a message to the driver can be triggered.

There Road bumps or obstacles in distance and altitude experience shows mostly stochastically distributed, must the o.g.

• – 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.

Calculated values are 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 _back -t _{front are} considered, in which only a single obstacle crossing is detected.
• - Only those time intervals t _back -t _are considered in _front , in which the temporal sequence of short consecutive obstacles is the same.
• - A message to the driver is only triggered when the R _dyn reduction was detected in a number of consecutive detection cases to be defined.
• - A message to the driver is only triggered if the R _dyn reduction has been determined up to a sum of accumulated detection cases to be defined.
• The detection algorithm is aborted as soon as the mean vehicle speed v _medium = A / (t _rear -t _front ) calculable from the time difference t _rear -t _forward and the 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 if the previously common uniform tacho calibration must be abandoned because the range of the roll The size of the tire that can be used on the vehicle becomes so large 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 (4)

System for detecting a tire pressure loss in motor vehicles while driving with means for detecting the wheel speed of each wheel, characterized in that at constant vehicle speed (v) for each wheel a variable proportional to the dynamic rolling circumference due to measured for a defined actual distance (A) Wheel speed of each individual wheel is determined, which is compared with a stored reference value. System according to claim 1, characterized in that the defined actual route (A) by a time window (t _back -t _front ) between two detectable events is predetermined, the beginning and end of the actual route mark. System according to claim 1 or 2, characterized that the defined actual Distance of the wheelbase (A) is. System according to one of the preceding claims, characterized in that the measurement of the wheel speed for a defined actual driving 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 begins and ends when a short time caused by the same road surface unevenness change of the wheel speed (n _back ) at least the rear wheel ends on the same side of the vehicle.