Method and system for tyre pressure surveillance for vehicles with anti-blocking systems (ABS systems)

0001The invention relates to a method for detecting the deviation of the tire pressure of at least one wheel from a reference value according to the preamble of claim 1 and a tire pressure monitoring system therefor according to the preamble of claim 8.

0002Safety and reliability are key factors in automotive engineering. The tire pressure plays an important role here; It has been found that tire pressure loss is a significant factor in road traffic accidents. 85% of the punctures are a consequence of a creeping pressure loss. A properly set tire pressure ensures, moreover, at all times optimal ride comfort with regard to rolling noise, vertical bumps and transverse joint sensitivity.

0003It is for example from ATZ 102 (200) 11, p. 950 ff. Known to measure the tire pressure directly by means of pressure sensors on two- or three-axle vehicles. The pressure sensors are attached to the tire and rotate with the wheel. The pressure sensors have a high-frequency transmitter (RF transmitter), which transmits the measured pressure values ​​to a receiver in the motor vehicle, which signals pressure losses to the driver. This method works both while driving and when the vehicle is stationary. Since this is a purely measuring method, the costs are relatively high, especially if all wheels are sensed.

0004It is also known from ATZ 94 (1992), pages 336-340, EP 0 489 562, EP 0 489 563 and EP 0 607 690 to monitor the tire pressure indirectly by means of the wheel sensors of anti-lock braking systems (ABS systems). The tire pressure affects the rolling circumference of the wheel. The determined by means of the wheel sensors of the ABS system wheel rotation speed depends on the rolling circumference of the wheel. If the wheel rotation speed of a wheel changes straight ahead and unrestrained relative to the reference speed of the other wheels or another wheel, this is an indication of a change in the rolling circumference of the wheel concerned as a result of a pressure loss of the tire or for a detachment of tire parts on the tire circumference or for a load change, each change of the rolling circumference is interpreted as a change in pressure. These known methods are relatively imprecise and can only detect relatively large and suddenly occurring pressure changes.

0005The invention is therefore based on the object to provide a method and system for tire pressure monitoring, which is inexpensive and more sensitive to minor and creeping pressure losses.

0006This object is solved by the embodiments of the invention indicated in claims 1 and 8. Advantageous developments of the invention are specified in the subclaims.

0007The method for tire pressure monitoring has the advantage that only a few conversion steps are required as a result of counting the distance covered when using conventional wheel sensors of ABS systems, in particular fewer conversion steps than in the known methods, and thereby greater accuracy can be achieved, especially at Use of digital computers. A smaller number of conversion steps has the advantage that is rounded less often in the course of the calculation or Less often decimal places are neglected in the calculation. Using the invention, this can advantageously be achieved by simply counting the distance pulses emitted by the wheel sensors, which are generated in proportion to the distance traveled.

0008According to advantageous developments of the invention, the counted distances of the individual wheels are each added diagonally to one another with respect to the wheel arrangement on the vehicle, and recognition of an undesired tire pressure condition takes place if the diagonal sums differ from one another by more than a predetermined limit value. In addition, the monitoring of the counted distances in several monitoring cycles, wherein the detection of an undesirable tire pressure condition occurs when the deviations of the diagonal sums exceeds a sum limit set for all monitoring cycles. This can further improve the accuracy and sensitivity in detecting unwanted tire pressure conditions.

0009The invention proposes in the embodiment of claim 8, a combination of direct tire pressure measurement by means of pressure sensors of a tire pressure and indirect tire pressure determination by measuring the rolling circumference dependent variables, such as wheel rotation speed and distance traveled, by means of wheel sensors of an existing ABS system. In this way it is possible to replace pressure sensors of the tire pressure measuring system by ABS wheel sensors and / or to use the ABS control device also for evaluating the measuring signals of the tire pressure measuring system, whereby components and costs can be saved without impairing the reliability and safety of the tire pressure monitoring. The actual tire pressures determined with the aid of the pressure sensors support the values ​​determined indirectly with the aid of the ABS system.

0010The invention will be explained in more detail with reference to the accompanying drawings, in which several embodiments of the invention are illustrated.

0011Show it<dl id="dl0001"><dt>Fig. 1-9</dt><dd>Various embodiments of the tire pressure monitoring device according to the invention in three-axle vehicles,</dd><dt>Fig. 10</dt><dd>a block diagram of an ABS control device with integrated control unit of a tire pressure measuring system,</dd><dt>Fig. 11</dt><dd>a block diagram of a means for determining distance and</dd><dt>Fig. 12</dt><dd>a diagram in which the counted by a counting register of the device of FIG. 11 period number is shown in dependence on the distance.</dd></dl>

0012The same components in the figures of the drawing are provided with the same reference numerals.

0013The drawing shows schematically in Figs. 1-9 equipped with antilock braking systems (ABS systems) 2 and Tire pressure measuring systems 12 Dreiachsfahrzeuge 4. The following statements apply mutatis mutandis to vehicles with (2 + n) axes with n ≥ 0, ie also for two-axle vehicles. The ABS systems and tire pressure measurement systems are combined into a tire pressure monitoring system.

0014The three-axle vehicles 4 each have a first axis A1, which here is the front axle and a right front wheel A1r and a left front wheel A1l has a second axis A2, here the drive axle and right twin wheels A2r and left twin wheels A2l has, and a third Axle A3, the right twin wheels A3r and left twin wheels A3l has.

0015Of course, instead of twin tires, a single tire may be available.

0016The ABS systems 2 include an ABS control unit 6 and a CAN interface 8. The wheels of at least one of the three axles A1, A2, A3 are schematically assigned wheel sensors and brake pressure modulators 25, 26, 27, 28, 29, 30 shown by a common block. The ABS control unit 6 determines the wheel rotation speed or the distance covered from the signals of the wheel sensors. A Rollradiusänderung by tire pressure loss is detected by an increasing Radrotationsgeschwindigkeit or decreasing distance and the driver displayed on a display 10. Influences by special situations, such as cornering, acceleration, deceleration, high speed, wheel load and abrasion, on the rolling radius and thus on the Radrotationsgeschwindigkeit or on the distance covered by suitable axle, pagewise and / or diagonal comparisons of Radrotationsgeschwindigkeit or distance and / or comparisons with thresholds compensated.

0017The tire pressure measuring system 12 has, for each wheel of at least one of the three axles, wheel electronics 31, 32, 33, 34, 35, 36, 37, 38, 39, 40 arranged in or on the tire and, as essential components, a sensor Signal processing stage, an RF transmitter stage and a battery as an energy source. Instead of the energy supply via a battery, an external energy supply by means of the transponder technology is also possible. The wheel electronics forms with the respective tire inflation valve a unit which is mounted on the rim. The sensor has a pressure sensor which measures the pressure in the tire and a device for measuring value acquisition and signal conditioning. The sensor controls a digital module in which the RF transmission stage is integrated, which transmits the measured data to a receiver / evaluation unit 42, if necessary with CAN interface 44, for example in the 433 MHz range. Each wheel electronics has its own identifier, which is transmitted during transmission. The set tire pressure is initialized by the driver or the system uses set pressures that are stored for the relevant vehicle type, whereby the system checks the set pressures for plausibility. A wheel replacement or change is detected by the system with regard to position on the vehicle. A tire pressure decrease - both at standstill and while driving - is displayed to the driver by the receiver / evaluation unit 42 on the display 10.

0018The Fig. 1 Fig. 12 schematically shows a tire pressure monitoring system utilizing a 6-channel ABS system 2 having wheel sensors and brake pressure modulators (shown as common blocks 25, 26, 27, 28, 29, 30) on all three axes, and a tire pressure measuring system 12 of ten Wheel electronics 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, wherein each wheel of each axle has a wheel electronics. The ABS system for the indirect determination of tire pressures and the tire pressure measuring system work in parallel and independently.

0019The Fig. 2 FIG. 12 shows a tire pressure monitoring system utilizing a 4-channel ABS system and different from the system of FIG. 1 differs in that only four sensors and four brake pressure modulators 25, 26, 27, 28 are provided for the first and second axes A1 and A2 and that the third axis for the ABS control is not sensed, but is controlled indirectly. The direct pressure measurement by the tire pressure measuring system 12 takes place as in the system according to FIG. 1 on all wheels of all axles. In the embodiment of FIG. 2 Saves two ABS wheel sensors and two ABS pole wheels.

0020The Fig. 3 schematically shows a tire pressure monitoring system in which the used for the tire pressure monitoring ABS system as shown in FIG. 2 four sensors and four brake pressure modulators 25, 26, 27, 28, on the first and second axes A1 and A2. Unlike the embodiments according to FIGS. 1 and 2, wheel electronics 33, 34, 35, 36, 37, 38, 39, 40 of the tire pressure measurement system 12 are provided only for the twin wheels of the second and third axles A2 and A3. At the wheels of the front axle A1 no wheel electronics are provided. Furthermore, unlike in FIGS. 1 and 2 the receiver / evaluation unit 42 of the tire pressure measuring system 12 integrated in the housing of the ABS control unit, wherein the ABS computer takes over the evaluation of the measurement signals of the wheel electronics. Thus, the wheel sensors and wheel poles are stored on the third axle and wheel electronics on the first axle as well as those in the embodiments according to FIGS. 1 and 2 separate evaluation device and CAN interface and the separate housing of the tire pressure measuring system. In this embodiment, a diagonal comparison is made of the sum of the wheel rotational speeds or travel distances of the right front wheel A1r and the left wheel of the second axle A2l with the sum of the wheel rotational speeds or travel distances of the left front wheel A1l and the right wheel of the second axle A2r. With tire pressure drop, the speed of the wheel in question will increase over the other wheels or will reduce the distance traveled accordingly. Positive values ​​then mean, for example, in the speed comparison, reduced pressure at the right front wheel A1r or left wheel A2l of the second axle; negative values ​​mean lower pressure on the left front wheel A1l or on the right wheel A2r of the second axle.

0021The diagonal comparison over the Radrotationsgeschwindigkeit or distance of the wheels of the first and second axis replaces the pressure sensors on the first axis.

0022Due to the diagonal comparison, the influence of curves is largely compensated. The absolute tire pressures determined by the wheel pressure sensors support the results from the diagonal comparison.

0023The Fig. 4 shows an embodiment of the tire pressure monitoring system according to the invention, which differs from the corresponding system of FIG. 3 differs in that wheel electronics 31, 32 are provided on the wheels A1r and A1l the first axis instead of the wheels of the second axis A2. The advantage over the embodiment of FIG. 3 is to be seen in the fact that the load / empty ratio at the first axis, the front axle, is less than at the second axis, so that on the first axis Rollradiusänderungen due to load changes make not so much noticeable as on the second axis or on the third axis.

0024The Fig. 5 shows an embodiment which differs from the embodiments according to FIGS. 3 and 4 differs in that the direct pressure measurement is made only on the twin tires of the third axis A3. A support of the indirect pressure determination via the diagonal comparison of the wheels of the first and the second axis by the direct pressure measurement on the third axis can be carried out here due to the spatial proximity of the second and the third axis to each other. Due to the spatial proximity is to be assumed in error-free case that the wheel speeds or Raddrehgeschwindigkeit of the wheels on the second and the third axis are substantially identical and thus the speed values ​​of the second axis can be transmitted to the third axis.

0025The Fig. 6 shows an embodiment of the tire pressure monitoring system, are provided in the wheel sensors 25, 26, 27, 28, 29, 30 of the ABS system 2 at the wheels of all three axes A1, A2, A3. A direct tire pressure measurement via wheel electronics 31, 32 is cost-saving only on the first axis A1, the front axle or Steering axle, provided. Unlike the embodiments according to FIGS. 1 and 2, in this embodiment, not single wheels but diagonal sums of the wheel speed signals or the travel distances of all the sensed axles are compared with each other. Curve influences are thereby largely compensated.

0026The following diagonal differences are formed in the speed comparison, where v is the speed:<maths id="math0001"><math display="block"><mrow><msub><mrow><mtext>Diagonal difference 1: (v</mtext></mrow><mrow><mtext>a1r</mtext></mrow></msub><msub><mrow><mtext> + v</mtext></mrow><mrow><mtext>A2l</mtext></mrow></msub><msub><mrow><mtext>) - (v</mtext></mrow><mrow><mtext>A1l</mtext></mrow></msub><msub><mrow><mtext> + v</mtext></mrow><mrow><mtext>A2r</mtext></mrow></msub><mtext>)</mtext></mrow></math><img file="EP1236588A2_D0001.tif" /></maths><maths id="math0002"><math display="block"><mrow><msub><mrow><mtext>Diagonal difference 2: (v</mtext></mrow><mrow><mtext>A2r</mtext></mrow></msub><msub><mrow><mtext> + v</mtext></mrow><mrow><mtext>A3l</mtext></mrow></msub><msub><mrow><mtext>) - (v</mtext></mrow><mrow><mtext>A2l</mtext></mrow></msub><msub><mrow><mtext> + v</mtext></mrow><mrow><mtext>A3r</mtext></mrow></msub><mtext>)</mtext></mrow></math><img file="EP1236588A2_D0002.tif" /></maths><maths id="math0003"><math display="block"><mrow><msub><mrow><mtext>Diagonal difference 3: (v</mtext></mrow><mrow><mtext>a1r</mtext></mrow></msub><msub><mrow><mtext> + v</mtext></mrow><mrow><mtext>A3l</mtext></mrow></msub><msub><mrow><mtext>) - (v</mtext></mrow><mrow><mtext>A1l</mtext></mrow></msub><msub><mrow><mtext> + v</mtext></mrow><mrow><mtext>A3r</mtext></mrow></msub><mtext>)</mtext></mrow></math><img file="EP1236588A2_D0003.tif" /></maths>

0027The evaluation of the diagonal difference formation yields the following: <tables id="tabl0001" num="0001"><table frame="all"><tgroup cols="4" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left"><b>Diagonal difference 1</b></entry><entry namest="col2" nameend="col2" align="left"><b>Diagonal difference 2</b></entry><entry namest="col3" nameend="col3" align="left"><b>Diagonal difference 3</b></entry><entry namest="col4" nameend="col4" align="left"><b>Downstream pressure</b></entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="right">positive</entry><entry namest="col2" nameend="col2" align="right">0</entry><entry namest="col3" nameend="col3" align="right">positive</entry><entry namest="col4" nameend="col4" align="center">a1r</entry></row><row><entry namest="col1" nameend="col1" align="right">negative</entry><entry namest="col2" nameend="col2" align="right">0</entry><entry namest="col3" nameend="col3" align="right">negative</entry><entry namest="col4" nameend="col4" align="center">A1l</entry></row><row><entry namest="col1" nameend="col1" align="right">negative</entry><entry namest="col2" nameend="col2" align="right">positive</entry><entry namest="col3" nameend="col3" align="right">0</entry><entry namest="col4" nameend="col4" align="center">A2r</entry></row><row><entry namest="col1" nameend="col1" align="right">positive</entry><entry namest="col2" nameend="col2" align="right">negative</entry><entry namest="col3" nameend="col3" align="right">0</entry><entry namest="col4" nameend="col4" align="center">A2l</entry></row><row><entry namest="col1" nameend="col1" align="right">0</entry><entry namest="col2" nameend="col2" align="right">negative</entry><entry namest="col3" nameend="col3" align="right">negative</entry><entry namest="col4" nameend="col4" align="center">A3r</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="right">0</entry><entry namest="col2" nameend="col2" align="right">positive</entry><entry namest="col3" nameend="col3" align="right">positive</entry><entry namest="col4" nameend="col4" align="center">A3l</entry></row></tbody></tgroup></table></tables>

0028By this Diagonalsummenvergleiche thus results in the possibility to realize a rad assigned to reduced pressure.

0029By way of example, the aforementioned formation of diagonal differences is also shown below for a four-axle vehicle, wherein only four diagonal differences are to be formed in a four-axle vehicle as well:<maths id="math0004"><math display="block"><mrow><msub><mrow><mtext>Diagonal difference 1: (v</mtext></mrow><mrow><mtext>a1r</mtext></mrow></msub><msub><mrow><mtext> + v</mtext></mrow><mrow><mtext>A2l</mtext></mrow></msub><msub><mrow><mtext>) - (v</mtext></mrow><mrow><mtext>A1l</mtext></mrow></msub><msub><mrow><mtext> + v</mtext></mrow><mrow><mtext>A2r</mtext></mrow></msub><mtext>)</mtext></mrow></math><img file="EP1236588A2_D0004.tif" /></maths><maths id="math0005"><math display="block"><mrow><msub><mrow><mtext>Diagonal difference 2: (v</mtext></mrow><mrow><mtext>A3r</mtext></mrow></msub><msub><mrow><mtext> + v</mtext></mrow><mrow><mtext>a4l</mtext></mrow></msub><msub><mrow><mtext>) - (v</mtext></mrow><mrow><mtext>A3l</mtext></mrow></msub><msub><mrow><mtext> + v</mtext></mrow><mrow><mtext>A4r</mtext></mrow></msub><mtext>)</mtext></mrow></math><img file="EP1236588A2_D0005.tif" /></maths><maths id="math0006"><math display="block"><mrow><msub><mrow><mtext>Diagonal difference 3: (v</mtext></mrow><mrow><mtext>a1r</mtext></mrow></msub><msub><mrow><mtext> + v</mtext></mrow><mrow><mtext>a4l</mtext></mrow></msub><msub><mrow><mtext>) - (v</mtext></mrow><mrow><mtext>A1l</mtext></mrow></msub><msub><mrow><mtext> + v</mtext></mrow><mrow><mtext>A4r</mtext></mrow></msub><mtext>)</mtext></mrow></math><img file="EP1236588A2_D0006.tif" /></maths><tables id="tabl0002" num="0002"><table frame="all"><tgroup cols="4" colsep="1" rowsep="1"><colspec colnum="1" colname="col1" colwidth="39.37mm" /><colspec colnum="2" colname="col2" colwidth="39.37mm" /><colspec colnum="3" colname="col3" colwidth="39.37mm" /><colspec colnum="4" colname="col4" colwidth="39.37mm" /><thead valign="top"><row><entry namest="col1" nameend="col1" align="left"><b>Diagonal difference 1</b></entry><entry namest="col2" nameend="col2" align="left"><b>Diagonal difference 2</b></entry><entry namest="col3" nameend="col3" align="left"><b>Diagonal difference 3</b></entry><entry namest="col4" nameend="col4" align="left"><b>Downstream pressure</b></entry></row></thead><tbody valign="top"><row><entry namest="col1" nameend="col1" align="right">positive</entry><entry namest="col2" nameend="col2" align="right">0</entry><entry namest="col3" nameend="col3" align="right">positive</entry><entry namest="col4" nameend="col4" align="center">a1r</entry></row><row><entry namest="col1" nameend="col1" align="right">negative</entry><entry namest="col2" nameend="col2" align="right">0</entry><entry namest="col3" nameend="col3" align="right">negative</entry><entry namest="col4" nameend="col4" align="center">A1l</entry></row><row><entry namest="col1" nameend="col1" align="right">negative</entry><entry namest="col2" nameend="col2" align="right">0</entry><entry namest="col3" nameend="col3" align="right">0</entry><entry namest="col4" nameend="col4" align="center">A2r</entry></row><row><entry namest="col1" nameend="col1" align="right">positive</entry><entry namest="col2" nameend="col2" align="right">0</entry><entry namest="col3" nameend="col3" align="right">0</entry><entry namest="col4" nameend="col4" align="center">A21</entry></row><row><entry namest="col1" nameend="col1" align="right">0</entry><entry namest="col2" nameend="col2" align="right">negative</entry><entry namest="col3" nameend="col3" align="right">0</entry><entry namest="col4" nameend="col4" align="center">A3r</entry></row><row><entry namest="col1" nameend="col1" align="right">0</entry><entry namest="col2" nameend="col2" align="right">positive</entry><entry namest="col3" nameend="col3" align="right">0</entry><entry namest="col4" nameend="col4" align="center">A3l</entry></row><row><entry namest="col1" nameend="col1" align="right">0</entry><entry namest="col2" nameend="col2" align="right">negative</entry><entry namest="col3" nameend="col3" align="right">negative</entry><entry namest="col4" nameend="col4" align="center">A4r</entry></row><row rowsep="1"><entry namest="col1" nameend="col1" align="right">0</entry><entry namest="col2" nameend="col2" align="right">positive</entry><entry namest="col3" nameend="col3" align="right">positive</entry><entry namest="col4" nameend="col4" align="center">a4l</entry></row></tbody></tgroup></table></tables>

0030In principle, any difference formation in which at least one axis of a diagonal difference is still included in another diagonal difference results in a unique wheel assignment. Starting with a five-time-one, a fourth diagonal difference is necessary.

0031The absolute tire pressures measured by the wheel electronics 31 and 32 on the first axle support the diagonal sum comparison.

0032The embodiment of FIG. 6 has particular advantages in the use of external tire pressure sensors, which can namely remain when changing complete wheels on the vehicle. It then does not need to be entered each time when changing the wheel, the wheel detection of the pressure sensor in the electronics via a suitable diagnostic device. The use of wheel electronics for measuring the absolute tire pressures only on the first axis (front axle or Steering axle) also has the great advantage that the costly tire pressure sensors can be omitted on the second and third axis. Otherwise one would have to build twin tire pressure sensors on the twin tires or one would have to connect two tire inflation connections via hoses, fittings and T-pieces consuming each other.

0033By measuring the absolute pressure on the wheels of the first axle, the two other axles can be compared more securely. In the Diagonalsummenvergleichen can be assumed by the pressure measurement on the first axis that at least two values ​​have a relation to the absolute pressure level, which would not be the case with the use of ABS wheel sensors, so that a cost-effective, reliable and secure tire pressure monitoring feasible is.

0034The Fig. 7 and FIG. 8 show embodiments of the invention, which differ from the embodiment according to FIG. 6 differ in that the absolute tire pressure is measured on two axes, on the wheels of the first axis A1 and the wheels of the second axis A2 (Fig. 7) as well as on the wheels of the first axle A1 and on the wheels of the third axle A3 (FIG. 8th). Although this means a greater structural complexity compared to the embodiment of FIG. 6; however, greater support is obtained for the results from the diagonal comparisons.

0035Fig. 9 shows an embodiment of the invention which fully corresponds to the embodiment of Fig. 1, except that a diagonal sum comparison is made according to the embodiments of Figs. 6-8.

0036The Fig. 10 schematically shows the integration of the receiver / evaluator 42 of the tire pressure measurement system 12 in the ABS control unit 6 of the ABS system. 2 In a common housing, the ABS control unit 6, the RF receiver 42 of the tire pressure 12, a stand-by micro-controller 50 and a common for both systems CAN interface 8 are arranged. The standby controller is always ready to receive the signals from the wheel electronics, even when the vehicle is parked, because the wheel electronics transmit constantly measured pressure values. This training is in the embodiments of the tire pressure monitoring device according to the invention according to FIGS. 3-8 provided. Reference numerals 25, 25 'and 10 and 31-40 schematically denote an ABS wheel sensor, an ABS control valve, a display and wheel electronics of the tire pressure measurement system.

0037With reference to FIG. 11 and 12 will be explained in more detail a means for determining the route. Voltages output by wheel sensors 25, 26, 27, 28 are filtered by input circuits 60 and converted into square-wave signals whose half or whole period lengths are evaluated by at least one micro-controller 62. Several micro-controllers can be used. In the drawing, for better understanding, only a micro-controller is drawn. The functions required for anti-lock / traction control (ABS / ASR) are designated by period duration measurement and speed calculation.

0038According to the invention, a path distance determination arranged in parallel is provided, which represents a counting register whose value is increased at each zero crossing of the sensor voltage. The distance can thus be determined in a simple manner by counting the periods of the sensor signals.

0039If the microcontroller 62 evaluates only whole periods or multiples thereof, then the odometer is incremented only at each corresponding zero crossing. If the micro-controller selects between these options as a function of the speed, it is favorable to choose the increase corresponding to the multiple of a half-period. The number of zero crossings depends on the tire rolling circumference and the number of teeth of the pole wheel. The numerical values ​​are constantly evaluated by a comparator 64 or only when the count register overflows with the highest count number reached.

0040Example: With a rolling circumference of 3,425 mm and a rotor with 100 teeth, each zero crossing represents a distance of 17,125 mm. After a fixed distance of z. B. 1 km, the achieved counts are compared. As a digitally simple measure, the evaluation of the achieved count values ​​can be triggered when the count leads to an overflow of the count register. For 16-bit count registers, the overflow occurs when the numerical value 65,535 (2¹⁶ - 1) is increased. 65,535 + 1 equals zero because the 17th digit of the binary number is not available, s. Representation in the diagram of FIG. 11. The count 2¹⁶ = 65,536 equals 1,122 km. This gives a resolution of 1/65536, corresponding to 0.0015%.

0041Investigations showed that the wheel speed increases by about 0.5% per bar pressure loss. This means that the period and thus the distance of a tooth decreases by about 0.5% per bar. Since 100 teeth represent the rolling circumference of the tire, this is also reduced by said value. The above favorable resolution (measurement accuracy) is in this example by a factor of 328 greater than the influence of the pressure reduction to be measured (per bar).

0042The achieved counting results are weighted. As is usual with ASR threshold crossing calculation, the difference of side wheels is rated higher than equiaxed or diagonally arranged wheels.

0043The route determination can be interrupted or aborted and restarted, z. B. when a transient driving situation is detected as anti-lock control, traction control, cornering or low-speed ride.

0044The device according to the invention for determining distances works independently of speed. There is no further effort required either to improve the speed calculation or To filter the result strongly in order to eliminate short-term fluctuations. The consideration of measurement inaccuracies, such as rounding errors in the velocity calculation omitted. The distance traveled by the wheel is determined directly, without the need for another arithmetic variable. The determined distance forms an integral, so that fluctuations of individual periods, caused z. B. due to road bumps, have no influence.