Boots – shoes – and leggings
Patent
1996-10-28
1998-03-17
Trammell, James
Boots, shoes, and leggings
364462021, 30312206, B60T 832
Patent
active
057294763
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
It is known that rotary speed sensors, especially wheel-speed sensors, which furnish information for safety-relevant systems such as ABS, must be monitored for malfunction. Malfunctions can occur if interference signals are input, or if line interruptions or the like occur.
Since the rotary speed is typically ascertained from the time between signal edges furnished by the sensor, an absent rotary speed sensor signal, in speed calculation for the time interval between two signal edges, would lead to an overly low rotary speed or wheel speed. In ABS systems, an improper pressure reduction at the affected wheel would then occur, leading to uncertainties.
For this reason, German Patent Application DE P 44 05 801.2 for instance proposes monitoring the output signal of the wheel-speed sensor, in an anti-lock brake system, to check on the one hand whether a plausible time has elapsed between individual pulses of the sensor signal. It is also monitored whether physically impossible variation values occur as the wheel runs up to speed. Dependent on this, two different comparison thresholds are made operative in alternation, depending on whether the wheel is found to be running up to speed continuously or not.
Other known versions for fast detection of absent sensor signals are based substantially on calculating an implausibly high wheel delay. An unfiltered wheel speed is then calculated from the time between the last two arriving edges of the sensor signal. If no edge appears for a certain period of time, then an edge that would arrive at that time in the most favorable case can be set theoretically. From a thus-constructed time interval, a new wheel speed can then be calculated. From the difference from the last wheel speed calculated before that, a certain wheel delay is then obtained.
Conversely, for every speed at a predetermined allowable wheel delay, a time interval can be determined within which the next edge must arrive. These methods of dynamic sensor monitoring involve more or less simplified interrogation, or interrogation adapted to the corresponding speed calculation, of a maximum allowable time period between two successive edges. One such method is also described in European Patent Disclosure EP 0 193 335 D1.
In the conventional methods, very pronounced wheel delays or corresponding times must be interrogated in order to prevent incorrect response. If the requisite monitoring thresholds are too high or monitoring times are too long, however, a sporadically occurring sensor interruption can no longer be detected. This is a disadvantage of the known methods, especially since in practice major wheel delays occur if braking is done from a high speed on a surface with a high coefficient of friction and if at the established input brake pressure there is an abrupt change to a very low coefficient of friction, such as if the wheel lifts away from the road surface.
ADVANTAGES OF THE INVENTION
The method of the invention having the characteristics of the main claim has the advantage over the prior art that it is secure against incorrect response of the error recognition in the event of simultaneously low monitoring thresholds or short monitoring times with which an actual sensor failure is intended to be detected. This is possible since a wheel relief or a transition to a low coefficient of friction never occurs suddenly.
It is accordingly especially advantageously possible to detect whether absent sensor signals are the consequence of a physical wheel delay or of an interruption in the sensor signal.
The advantages are attained in that dynamic sensor monitoring is done in which filtered and unfiltered variables are monitored for plausibility. Advantageously, these variables are the unfiltered wheel speed, the filtered wheel speed, and the filtered change (derivation) in the wheel speed or in other words the filtered acceleration.
Further advantages of the invention are attained with the aid of the provisions recited in the dependent claims.
DRAWING
One exemplary embodiment of the invention
REFERENCES:
patent: 5099443 (1992-03-01), Higashimata
patent: 5479556 (1995-12-01), Oh
patent: 5556174 (1996-09-01), Wiss et al.
patent: 5583772 (1996-12-01), Pfau
Robert & Bosch GmbH
Striker Michael J.
Trammell James
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