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US 4,226,219 AGranted
Engine timing circuit with noise immunity
AssigneeRCA Corporation
InventorJohn A. Olmstead
Life of this patent
Estimating the term…
Abstract
An electronic timing circuit for an internal combustion engine includes a Schmitt trigger operated by timing pulses from a magnetic pick-up mounted on the engine. The upper trip point is set high when the pulses have a high amplitude due to a high engine speed, so that false triggering of the circuit by noise of lower amplitude is avoided. A lower trip point is automatically set when the pulses have a low amplitude, such as when the engine is cranked to start it.
Claims4
In an electric timing system for an internal combustion engine,
- a magnetic pick-up positioned on the engine to produce a signal waveform in which each cycle has a gradual up slope and steep down slope,
- a Schmitt trigger including a voltage divider, and including a comparator having an input receptive to said signal waveform, and having a reference input and an output connected to taps on said voltage divider, so that the Schmitt trigger produces an output pulse having a leading edge when the input signal on the up slope reaches an upper trip point and having a trailing edge when the input signal on the down slope reaches a lower trip point,
- a transistor having output electrodes defining a conduction path connected across a portion of said voltage divider, and
- means operative at low engine cranking speeds when the signal waveform cycles have a lower peak amplitude to render said transistor conductive and thereby reduce the upper trip point of said Schmitt trigger.
1 more element
Dependencies are inferred from the claim text.