FAILURE DETECTION BY PERIOD COMPARISON

• US 3,803,425 A
• Filed: 05/03/1973
• Issued: 04/09/1974
• Est. Priority Date: 05/03/1973
• Status: Expired due to Term

• Current Assignee: Siemens-Bendix Automotive Electronics LP
• Original Assignee: Ralph W. Carp
• Inventors: Carp, Ralph W.
• Primary Examiner(s): Heyman, John S.
• Application Number:
  US05/356,870
• Time in Patent Office: 341 Days
• Field of Search: 307/204,219,233,235 328/133,134
• US Class Current: 327/82
• CPC Class Codes: B60T 2270/416 Wheel speed sensor failure
• CPC Class Codes: B60T 8/885 using electrical circuitry

Abstract

A circuit which provides a failure indication when one of two speed sensors in an adaptive braking system fails includes a pair of comparators for comparing the outputs of each sensor individually against a predetermined reference. When the output from one of the sensors exceeds its reference, it generates a feedback signal to change the reference of the other comparator to a new value. A failure is indicated if one sensor exceeds the predetermined reference and the second sensor output fails to exceed the new value of the reference.

Claims

1. Means for detecting a failure to one of first and second wheel speed sensor means, each of which said sensor means normally generates an electrical pulse train having a pulse repetition frequency proportional to the speed of a sensed wheel, said wheel speed sensor means being disposed in first and second channels, respectively, and each said channel comprising:

means for generating a voltage ramp from a first voltage level towards a second voltage level;

means responsive to a predetermined, cyclically recurring point of said pulse train for returning said voltage ramp to said first voltage level;

means for generating a reference voltage level proportional to a relatively high sensed wheel speed;

a retriggerable one-shot;

a comparator for triggering said one-shot when the instantaneous value of said voltage ramp attains said reference voltage level, said one-shot thereby generating a one-shot output signal;

means responsive to said one-shot output signal for altering the reference voltage level at the other channel to be proportional to a relatively low sensed wheel speed;

means responsive to a one-shot signal of one channel and the absence of a one-shot signal from the other channel for generating a second signal; and

, means responsive to a predetermined continuous time duration of said second signal for generating a failure signal which is indicative of a failure in at least one of said sensor means.

2. Means for detecting a failure as recited in claim 1 wherein said means for generating a reference voltage level comprises a d.c. power source and a voltage divider connected thereacross, said reference voltage level being obtained from a point interior thereof, and wherein said means for altering comprises a resistance means switchably connected into the voltage divider of said other channel in response to said one-shot output signal.

3. Means for detecting a failure as recited in claim 2 wherein said comparator includes an output terminal and wherein said retriggerable one-shot comprises:

an amplifier having an input terminal connected to said comparator output terminal and an amplifier output terminal, said one-shot output signal being generated at said amplifier output terminal;

a capacitor connected between said amplifier input terminal and a terminal of said d.c. power source; and

, resistor means connected across said capacitor.

4. Means for detecting a failure as recited in claim 3 wherein said comparator supplies current to said capacitor when triggering and retriggering said one-shot but where said comparator does not sink current into its output terminal, and wherein said amplifier is characterized by a high input impedance input terminal whereby the only effective discharge path of said Capacitor is through said resistor means.

5. Means for detecting a failure as recited in claim 1 wherein said means for generating a second signal comprises an exclusive OR gate and said means for generating a failure signal comprises a time constant circuit.

6. In an adaptive braking system including at least first and second wheel speed sensors for generating electrical signals proportional to first and second sensed wheel speeds respectively, means for indicating a failure when the signal from one of said sensors indicates a wheel speed above a first threshold for a predetermined period of time while simultaneously the signal from the other of said sensors indicates a wheel speed below a second threshold, comprising:

means for generating a reference signal proportional to said first threshold;

first means responsive to said reference signal for generating a first signal when the signal generated by said first sensor is proportional to a first wheel speed in excess of said first threshold;

second means responsive to said reference signal for generating a second signal when the signal generated by said second sensor is proportional to a second wheel speed in excess of said first threshold;

cross-coupled feedback means between said first and second means for changing the reference signal at one of said first and second means when the other of said first and second means generates its output signal to a second reference signal proportional to said second threshold, said one of said first and second means being thereby responsive to said second reference signal for generating its output signal when the signal generated by its associated sensor is proportional to a wheel speed in excess of said second threshold; and

, means responsive to the generation of one of said first and second signals for said predetermined period of time while simultaneously the other of said first and second signals is not generated for providing a failure signal.

7. The means for indicating of claim 6 wherein said means for generating a reference signal comprises a d.c. power source and first and second voltage dividers connected thereacross, said reference signal being obtained from first and second points interior of said first and second voltage dividers respectively.

8. The means for indicating of claim 7 wherein said cross-coupled feedback means comprises:

first resistor means switchably connected into said second voltage divider in response to said first signal; and

, second resistor means switchably connected into said first voltage divider in response to said second signal.

9. The means for indicating of claim 7 wherein said means for providing a failure signal comprises:

an exclusive OR gate responsive to said first and second signals for generating an output signal; and

, a time constant means responsive to said exclusive OR gate output signal for providing said failure signal.

10. The means for indicating of claim 9 wherein said cross-coupled feedback means comprises:

first resistor means switchably connected into said second voltage divider in response to said first signal; and

, second resistor means switchably connected into said first voltage divider in response to said second signal.