DE4014315A1 - Frequency counter surveillance for vehicle braking system - Google Patents

Abstract

A frequency counter monitoring system takes its input from an inversely proportional sensor (1) detecting, e.g. wheel speed, being fed via a digitiser (2) to the frequency counter (31) in a processor block (3). To determine the validity of the count, a comparison is made with an average count value by digitising the same signal to a fixed width and amplitude (4), low-pass filtering (5) and analogue-to-digital conversion (32). The comparator/limiter (33) produces an output (34) to activate a warning signal or shutdown if the deivation exceeds a certain max. level.

Description

State of the art

In ABS / ASR systems that use two µ processors per channel for redundancy reasons, it is customary to compare the frequency measurement results of the two digital frequency measuring devices with one another and to indicate an error in the event of deviations or to generate a shutdown signal. The Frequency measurement direction are based, for. B. on the counting of the distance T of the pulses of the speed sensor and on the expression 1 / T.

Advantages of the invention

The device according to the invention allows a second µ processor or to waive a corresponding expansion of the existing µ processor.

Figure description

The drawing shows an exemplary embodiment of the invention. There, a wheel speed signal indicative donating sensor 1 is designated 1, the signals are converted in a block 2 in square-wave signals. These are fed to the digital input of a μ-processor 3 , in the interior of which only the blocks necessary in connection with the invention are shown.

If the invention is used in an ABS and / or ASR, it additionally contains che blocks to slip and accelerate from the wheel speed signals / To generate deceleration signals and finally brake pressure control signals.

In a block 31 , the frequency or speed of the wheel is obtained as a digital value from the incoming pulses by counting and forming the reciprocal value.

This digital value should be checked for correctness. For this purpose, however, a second module corresponding to block 31 is not used, but an analog, completely different frequency measurement method is used. For this purpose, the output pulses of block 2 are converted in a block 4 into pulses of constant width and height, the width of which is dimensioned such that there is still a distance between adjacent pulses even at the highest frequency to be processed. These pulses are then fed to a low-pass filter 5 , which outputs the mean value of the input signal at its output. This is proportional to the input frequency. The analog signal is fed via an analog input of the μ-processor into an analog-digital converter 32 , the digital output value of which is compared in a comparator 33 with the digital value determined in block 31 . If the values differ from one another, a warning and / or switching signal for switching off the control is emitted via line 34 .

Claims (2)

1. Monitoring device for a digital frequency measuring device, to which the pulses emitted by a sensor, the distance of which is inversely proportional to the frequency to be measured, and which delivers a digital measurement result, the frequency determined being monitored for accuracy by comparison, and from a deviation A certain size an error is displayed, characterized in that the pulses emitted by the sensor are additionally converted into pulses of the same width and height, that these converted pulses are passed through a low pass, that the output signal of the low pass is converted into a digital signal and that two digital measurement results of the frequency determined in different ways are compared with one another. 2. Monitoring device according to claim 1, characterized by its Use in ABS / ASR systems with only one digital frequency measurement Facility.