Patent ID: 6043660
Filing Date: 2000-03-28
Classification: F02P

Abstract:
A circuit arrangement for measuring an ion current in a combustion chamber of an internal combustion engine during an ion current flow phase between ignition phases, comprising at least one ignition transformer including a primary winding and a secondary winding, a spark plug connected between a high voltage end of said secondary winding and ground, an inverting amplifier (3) connected with an input to a low voltage end of said secondary winding for producing a constant measuring voltage applied to said secondary winding during at least one of said ion current flow phases for generating an ion current in said combustion chamber, and a first resistor (R.sub.1) connected so that said ion current causes a proportional voltage drop across said first resistor (R.sub.1) for measuring said ion current, said circuit arrangement further comprising a diverting circuit including a first diverting branch (A.sub.1) comprising a first semiconductor diode (D.sub.1) connected between ground and said low voltage end of said secondary winding for dissipating negative high voltage peaks, and a second diverting branch (A.sub.2) connected in parallel to said inverting amplifier (3), said second diverting branch (A.sub.2) comprising a series connection including an ignition current measuring second resistor (R.sub.2 or R.sub.2 '), a second semiconductor diode (D.sub.2) and a controllable semiconductor switch (T), said series connection being connected to ground, said semiconductor switch (T) having a control input connected to an output of said inverting amplifier (3) for switching said semiconductor switch (T) to the ""ON"" state and thereby shunting an ignition current flowing during said ignition phase to ground through said series connection.