Allocation method for a combined tire pressure monitoring system in a motor vehicle

The present invention relates to an allocation method for a tire pressure monitoring system in motor vehicles combining directly and indirectly monitoring tire inflation pressure.

Systems which enhance the active or passive safety are used at an increasing rate in up-to-date vehicles. As experience shows, many accidents are caused by defective vehicle tires. A large number of these tire defects are due to a wrong tire inflation pressure or a stealthy inflation pressure loss in the tire. Therefore, it is of great significance in terms of safety of the vehicle to reliably monitor the tire inflation pressure.

Two types of tire inflation pressure monitoring systems have become known so far. On the one hand, so-called directly measuring tire pressure monitoring systems (TPMS: Tire Pressure Monitoring System) as described e.g. in DE 199 26 616 C2 or in DE 199 38 431 C2, and so-called indirectly measuring tire pressure monitoring systems (DDS: Deflection Detection System) as described e.g. in DE 100 58 140 A1 are known in the art.

The tire pressure monitoring system with direct measurement (TPMS) measures the respective tire inflation pressure by means of pressure modules directly in the tire concerned, with the result that all wheels are monitored irrespective of each other. The measured tire inflation pressure is sent alone or in conjunction with other measured values (e.g. temperature of the tire) to one or more receiving units arranged at the vehicle, using a transmitting unit which is connected to the pressure measuring module. In this respect, each transmitting unit includes an individual identification code which is sent together with the measured tire inflation pressure and any possible other measured values. The receiving unit which is provided one time or several times relays the data received (measured values and identification codes) to an evaluating device which emits a warning to the driver when tire pressure loss prevails. The direct measurement of the tire inflation pressure permits the directly measuring tire pressure monitoring system (TPMS) to detect tire inflation pressure loss at a very early time already.

The directly measuring tire pressure monitoring system known in the art suffers from the shortcoming that the reliability is very limited on account of the fact that the pressure measuring modules usually are not designed redundantly, on the one hand, while, on the other hand, great expenditure is needed for detecting which tire (e.g. front left tire) suffers from a loss in inflation pressure, because several receiving units are generally necessary to this end in order to achieve a safe allocation of the tires to the installation positions (e.g. front left).

The tire pressure monitoring system with indirect measurement (DDS) is based on the measurement of rotational wheel speeds. The increase in rotational wheel speeds is a standard of the tire inflation pressure because a tire having a lower tire inflation pressure (e.g. 1.0 bar) that differs from the nominal pressure (e.g. 2.0 bar) exhibits a smaller dynamic rolling circumference. Due to this difference in rotational speeds, the tire pressure monitoring system with indirect measurement (DDS) detects tire inflation pressure loss. To determine the rotational wheel speeds, typically those wheel sensors are used which are already provided in a vehicle with an anti-lock system (ABS). These wheel speed sensors are favorable because they are monitored in terms of possible malfunctions or are designed redundantly, with the result that tire inflation pressure loss is detected with a high rate of reliability. As the installation position (e.g. front left) of the wheel sensors is known to the tire pressure monitoring system with indirect measurement (DDS), the allocation of a wheel with tire inflation pressure loss to its installation position is simple. Further, this system is very moderate in price because the necessary wheel sensors are already mounted at least in vehicles equipped with ABS.

It is disadvantageous in the known tire pressure monitoring system with indirect measurement (DDS) that a simultaneous tire inflation pressure loss on all wheels cannot be detected because a difference in the rotational speeds of the wheels cannot be detected in the event of a simultaneous tire inflation pressure loss.

Further, there are combined tire pressure monitoring systems linking a tire pressure monitoring system with direct measurement to a tire pressure monitoring system with indirect measurement. A combined tire pressure monitoring system of this type is described in DE 101 52 338 A1. The prior-art combined tire pressure monitoring system, for cost reasons, manages without taking into account the individual identification code, which is usually sent along with the measured tire inflation pressure and any possible other measured valued from the transmitting unit connected to the pressure measuring module to the receiving unit. It is disadvantageous in this arrangement that in case two or more vehicles are placed side by side, the evaluating device is unable to identify which tire inflation pressure sent belongs to the own vehicle.

In view of the above, an object of the invention is to provide an allocation method for a combined tire pressure monitoring system which permits a low-cost and reliable allocation of the vehicle wheels to the respective installation positions.

According to the invention, this object is achieved by an allocation method taking into consideration established probability values W_IDx_y describing a frequency distribution which indicates how often pressure measuring modules with the identification codes IDx are identified as pertaining to the installation positions y.

In a favorable embodiment of the allocation method of the invention, a counter C_IDx_y is made available for each possible combination of a pressure measuring module with an identification code IDx and an installation position y.

In another preferred embodiment of the allocation method, an identification code counter C_IDx is initialized for each pressure measuring module with an identification code IDx.

Further features and advantages of the allocation method of the invention will be described in the following by making reference to an embodiment.

In the drawing,

FIG. 1 shows a combined tire pressure monitoring system according to the present invention.

The combined tire pressure monitoring system is herein based on a tire pressure monitoring system with direct measurement (TPMS) and a tire pressure monitoring system with indirect measurement (DDS).

The tire pressure monitoring system with direct measurement (TPMS) uses a transmitting unit arranged in or at the vehicle wheel to send wheel-individual tire inflation pressures together with individual identification code, hereinbelow referred to as IDx, to a receiving unit connected to an evaluating device. As this occurs, the tire inflation pressures of each individual wheel are sensed by so-called pressure measuring modules. Thus, the evaluating device receives from each vehicle wheel an individual tire inflation pressure and an individual identification code (IDx). The directly measuring tire pressure monitoring system of the invention includes a pressure measuring module per wheel. If fewer pressure measuring modules than wheels are provided, the tire inflation pressures of the remaining wheels can be found out in this case by means of the tire pressure monitoring method with indirect measurement that will be described hereinbelow.

The tire pressure monitoring system with indirect measurement (DDS) detects a tire inflation pressure loss from rotational wheel speeds being measured by means of wheel sensors. Usually the wheel sensors which are already used in a vehicle equipped with ABS to determine the rotational performance of the wheels are also used for the tire pressure monitoring system with indirect measurement (DDS). In this case, the wheel sensors have already been allocated to an installation position, e.g. wheel sensor at the front left wheel. Hence, it is also known to the tire pressure monitoring system with indirect measurement (DDS) at which installation position a tire inflation pressure loss is identified.

The tire pressure monitoring system with direct measurement (TPMS) detects when at least one tire inflation pressure is changing. This change of the at least one tire inflation pressure is also detected by the tire pressure monitoring system with indirect measurement (DDS). The information of both systems is processed statistically in order to establish an allocation of the IDx (from TPMS) to the wheel positions (from DDS).

Thresholds are defined to detect tire inflation pressure loss and the tire pressure monitoring system (TPMS) with direct measurement identifies tire inflation pressure loss when values drop below the above thresholds. For example, a normal tire inflation pressure of 2.0 bar is taken as a basis. A tire inflation pressure of 1.5 bar is e.g. defined as a threshold. When one pressure measuring module or several pressure measuring modules furnish a tire inflation pressure ranging below the threshold of 1.5 bar, the evaluating device concludes tire inflation pressure loss. Now a check is made whether the tire pressure monitoring system with indirect measurement (DDS) detects the installation position of the wheels concerned. To this end, a counter C is initialized for each possible combination of the individual identification code (IDx) of the pressure measuring modules and the installation positions. With four installation positions y (VL: front left; VR: front right; HL: rear left; HR: rear right) and four pressure measuring modules IDx (ID 1 : identification first pressure measuring module; ID 2 : identification second pressure measuring module; ID 3 : identification third pressure measuring module; ID 4 : identification fourth pressure measuring module), 16 counters C_IDx_y will thus result in total. For example, C_ID 1 _VL means that the counter of the identification code ID 1 in a combination with the left front wheel is concerned. In addition, four identification code counters C_IDx (x: 1, 2, 3, 4) are made available which find out how frequently a change in pressure is supplied by a pressure measuring module with the pertinent identification code (IDx).

If, for example, the pressure measuring module with the identification code ID 1 indicates a tire inflation pressure loss and the tire pressure monitoring system with indirect measurement (DDS) detects e.g. at the installation position left front (VL) likewise a tire inflation pressure loss, the counter C_ID 1 -VL will be raised by a defined value (e.g. ‘1’). Further, the identification code counter C_ID 1 is also raised by a defined value (e.g. ‘1’). When two pressure measuring modules indicate changes in pressure (e.g. ID 1 and ID 2 ) and the tire pressure monitoring system with indirect measurement (DDS) detects a change in pressure at two wheels (e.g. VL and VR), then the counters for all combinations possible in this case will be counted upward by ‘0.5’ (in our example C_ID 1 _VL, C_ID 1 _VR, C_ID 2 _VL, C_ID 2 _VR). Further, all possible combinations (C_ID 3 _HL, C_ID 3 _HR, C_ID 4 _HL, C_ID 4 _HR) of the remaining identification codes (ID 3 and ID 4 ) with the remaining installation positions (HR and HL) are raised by ‘0.5’ because these combinations are bound to occur when the identification codes ID 1 and ID 2 are allocated to the installation positions VL and VR. In addition, all identification code counters (C_ID 1 , C_ID 2 , C_ID 3 and C_ID 4 ) are also raised by ‘1’ in each case.

When three pressure measuring modules show a change in pressure (e.g. ID 1 , ID 2 and ID 3 ) and the tire pressure monitoring system with indirect measurement (DDS) detects three installation positions (e.g. VL, VR and HL) where a change in pressure prevails, the installation position of the fourth wheel will be allocated undoubtedly thereby. In the example, the pressure measuring module with the identification code ID 4 does not show a change in pressure, and no change in pressure was identified at the installation position HR. Thus, the counter C_ID 4 _HR for this combination and the identification code counter C_ID 4 are respectively counted upward by ‘1’.

When one (or more) of the identification code counters (C_ID 1 , C_ID 2 , C_ID 3 or C_ID 4 ) reaches or exceeds a predetermined maximum value C_IDmax (e.g. C_ID 1 >C_IDmax), then four probability values W_ID 1 _y (y: VL, VR, HL, HR) are calculated for these identification code ID 1 . In our example, the following probability values are calculated:

The allocation of an identification code (IDx) to an installation position y occurs when a probability value W_IDx_y exceeds a probability threshold Wmax and is considerably higher than all other calculated probabilities. For example, the following probabilities or dependencies result:

W_ID 1 _VL>Wmax W_ID 1 _VL>>W_ID 1 _VR and W_ID 1 _VL>>W_ID 1 _HL and W_ID 1 _VL>>W_ID 1 _HR

Thus, the pressure measuring module with the identification code ID 1 is allocated to the installation position left front (VL).

The counters (C_IDx and C_IDx_y) mentioned in the allocation method of the invention represent only one embodiment for determining the required probability values W_IDx_y. Of course, other known methods such as the setting of a flag, etc., can be employed in order to determine a frequency distribution between the pressure measuring modules with the identification codes IDx and the installation positions y. Besides, it is not imperative to provide 16 counters C_IDx_y. It is also sufficient, yet with a slightly lower rate of detection reliability than in the embodiment mentioned above, to consider only 12 counters C_IDx_y, in which case only three pressure measuring modules are allocated to their installation positions. The fourth pressure module would be allocated automatically to the remaining installation position in such a case.