Automotive vehicle catalyst diagnostic
First Claim
1. An engine control and diagnostic method for varying the source of an actual air/fuel ratio feedback signal in an automotive internal combustion engine having an exhaust system including at least an upstream and a downstream catalytic treatment device for catalytically treating engine exhaust gas passing therethrough, comprising the steps of:
- during a diagnostic period, sensing a treated oxygen content of exhaust gas after such exhaust gas has been catalytically treated by the upstream catalytic treatment device;
during engine operating periods other than the diagnostic period, sensing a substantially untreated oxygen content of engine exhaust gas prior to such exhaust gas being catalytically treated by at least the upstream and downstream catalytic treatment devices;
controlling engine air/fuel ratio in response to the sensed treated oxygen content during the diagnostic period; and
controlling engine air/fuel ratio in response to the sensed substantially untreated oxygen content during engine operating periods other than the diagnostic period.
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Accused Products
Abstract
A catalytic treatment device diagnostic for an automotive exhaust system having at least two catalytic treatment devices wherein reduced oxygen storage capacity of each of the devices may be diagnosed without significant loss in engine air/fuel ratio control precision by varying the source of an actual air/fuel ratio feedback signal from a sensor positioned upstream of the devices during normal operation to a sensor mounted downstream of at least one of the devices during a diagnostic period. Measurable change in the oxygen content of exhaust gas passing through each of such devices then becomes available for analysis during the diagnostic period.
55 Citations
13 Claims
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1. An engine control and diagnostic method for varying the source of an actual air/fuel ratio feedback signal in an automotive internal combustion engine having an exhaust system including at least an upstream and a downstream catalytic treatment device for catalytically treating engine exhaust gas passing therethrough, comprising the steps of:
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during a diagnostic period, sensing a treated oxygen content of exhaust gas after such exhaust gas has been catalytically treated by the upstream catalytic treatment device; during engine operating periods other than the diagnostic period, sensing a substantially untreated oxygen content of engine exhaust gas prior to such exhaust gas being catalytically treated by at least the upstream and downstream catalytic treatment devices; controlling engine air/fuel ratio in response to the sensed treated oxygen content during the diagnostic period; and controlling engine air/fuel ratio in response to the sensed substantially untreated oxygen content during engine operating periods other than the diagnostic period. - View Dependent Claims (2, 3, 4, 5, 6, 7)
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8. An engine control and diagnostic method for an internal combustion engine from which exhaust gas exits into an exhaust gas flow path which includes an upstream and a downstream catalytic treatment device, wherein the engine exhaust gas passes from the engine, through the upstream catalytic treatment device and then through the downstream catalytic treatment device, comprising the steps of:
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sensing an upstream oxygen content of engine exhaust gas passing between the engine and the upstream catalytic treatment device; sensing an intermediate oxygen content of engine exhaust gas passing between the upstream and downstream catalytic treatment devices; sensing a downstream oxygen content of engine exhaust gas after such exhaust gas exits the downstream catalytic treatment device; during a predetermined diagnostic period, to allow for upstream and downstream catalytic treatment device diagnostics, deriving a value representing actual engine air/fuel ratio as a predetermined function of the sensed intermediate oxygen content; during periods other than the predetermined diagnostic period, deriving a value representing actual engine air/fuel ratio as a predetermined function of the sensed upstream oxygen content; and controlling engine air/fuel ratio so as to drive the derived actual air/fuel ratio toward a predetermined desired air/fuel ratio. - View Dependent Claims (9, 10, 11, 12)
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13. An engine control system for controlling internal combustion engine air/fuel ratio and for diagnosing fault conditions in at least two catalytic treatment devices in a flow path in which internal combustion engine exhaust gas flows from the engine through a first catalytic treatment device and then through a second catalytic treatment device, comprising:
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an upstream sensor positioned in the flow path to sense an upstream oxygen content of exhaust gas passing between the engine and first catalytic treatment device; an intermediate sensor positioned in the flow path to sense and output a signal indicating an intermediate oxygen content of exhaust gas passing between the first and second catalytic treatment devices; a downstream sensor positioned in the flow path to sense and output a signal indicating a downstream oxygen content of exhaust gas passing between the second catalytic treatment device and the atmosphere; a controller responsive to an input signal indicating actual engine air/fuel ratio to control at least a predetermined one of engine inlet air and engine inlet fuel to the engine to drive the actual engine air/fuel ratio toward a desired air/fuel ratio, wherein the input signal corresponds to the output signal from the intermediate sensor during a predetermined test period, and wherein the input signal otherwise corresponds to the output signal from the upstream sensor; and a diagnostic device which receives the output signal from at least the intermediate and downstream sensors for diagnosing fault conditions in the first and second catalytic treatment devices.
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Specification