Method and apparatus for determining engine oil change intervals according to actual engine use

A lubricating oil change indicating system for an internal combustion engine comprising:

• means for sensing the speed of engine operation and outputting electrical pulses at a rate proportional to said engine speed;
• means for sensing the temperature of the lubricating oil;
• means for measuring the time the engine is in continuous operation above a predetermined speed;
• means for periodically sampling the temperature sensing means and said time measuring means and outputting a then current weighting factor according to predetermined levels of sensed temperature and the continuous time said engine has been in operation above said predetermined speed;
• means for multiplying each output pulse from said speed sensing means by the then current weighting factor to produce a corresponding weighted pulse value;
• means for accumulating the weighted pulse values to produce an accumulated pulse value;
• means for comparing the accumulated pulse value with a predetermined value that corresponds to a prescribed wear limit for said lubricating oil;
• means for signaling an indication of the necessity for changing the lubricating oil when said comparing means determines that said accumulated pulse value exceeds said predetermined value;
• and
• means for resetting said time measuring means whenever said speed sensing means outputs pulses at a rate that is proportional to an engine speed below said predetermined speed.