Soft linear O2 sensor

Details Soft linear O2 sensor Soft linear O2 sensor

2000-10-16

2002-11-19

Mancene, Gene (Department: 3747)

Internal-combustion engines

Charge forming device

Including exhaust gas condition responsive means

Reexamination Certificate

active

06481427

ABSTRACT:

TECHNICAL FIELD
This invention pertains to closed loop microprocessor control of air-to-fuel mass ratio (A/F) in a fuel-injected automotive internal combustion engine using feedback signals from the vehicle's exhaust oxygen (O
2
) sensor. More specifically, this invention pertains to a process for modifying the operation of the vehicle fuel control system to change the on-off, nonlinear response of the exhaust O
2
sensor to a more useful proportional response around the stoichiometric A/F. The present invention is driven by the need to operate the engine slightly rich or slightly lean for their respective emissions advantages during hot or cold engine operation.
BACKGROUND OF THE INVENTION
Most current production exhaust oxygen sensors (EOS) are zirconia-based, solid electrolyte, electrochemical devices that are used in conjunction with three-way catalytic converters to precisely control exhaust air-fuel ratio and to reduce vehicle tailpipe emissions. These robust sensors have been used for many years with powertrain control modules (PCM) for closed-loop computer control of fuel injector(s) in supplying gasoline to the cylinders of the engine in amounts near the stoichiometric A/F. The stoichiometric A/F is approximately 14.7 for most common gasoline fuels available in the market today. The PCM is programmed for engine operation near the stoichiometric A/F for best performance of the catalytic converter.
Such oxygen sensors are heated by exhaust gas or an additional power supply and produce a relatively low voltage (0.0 V to approximately 0.5 V) at A/F higher than stoichiometric value and a high voltage (0.5 V to 1.0 V) at lower A/F ratios. Around the stoichiometric A/F, the response of these sensors is unreliable and indeterminate in the manner in which they have been used. Therefore, the sensor steady state characteristic response to the exhaust mixture variations is unusable when the combustion mixture of air and fuel changes from slightly rich of stoichiometric A/F to slightly lean, or vice versa. In other words, in this region the magnitude of the voltage signal from the zirconia electrolyte oxygen sensor cannot presently be used by the PCM as indicative of the precise A/F. Instead, the O
2
sensor is treated by the PCM as an on-off device, or simply as a fuel lean or fuel rich indicator (with respect to stoichiometric A/F). The PCM is programmed to respond, at a fixed rate, by changing the duration of the next fuel injection event to compensate for the present fuel lean or rich indicating signal.
Depending upon engine speed and the number of engine cylinders, the PCM must command a fuel injection amount into the intake port of a cylinder, or into a cylinder, many times per second. By considering the current and recent past O
2
sensor voltage values to adjust the duration of the next fuel injection event, the PCM delivers an almost average stoichiometric A/F to the engine. However, because of the on/off nature of the sensor signal, the engine is essentially just cycling around stoichiometric A/F. Such an “averaged” A/F closed-loop control achieves significant reductions in emissions of unburned hydrocarbons, carbon monoxide and nitrogen oxides as compared to a pre-programmed PCM using the open-loop control and without actual feedback from downstream exhaust information. However, further reductions in tailpipe emissions are required in the recent government-mandated emission standards. Therefore, more precise A/F management and fuel control is now essential.
Accordingly, it is an object of this invention to provide a process for changing the switch-like output of the venerable zirconia-type oxygen sensor to a proportional response around the stoichiometric A/F. This newly created linear range in the output of the production O
2
sensors would allow the current PCM, or fuel controller, to manage engine operation closer to the desired air-to-fuel ratio (slightly lean or rich of stoichiometric) and achieve further emission reductions with essentially the current production hardware.
SUMMARY OF THE INVENTION
The oxygen content in the combustion products of a hydrocarbon-fuel engine depends significantly on the proportions of air and fuel supplied to the cylinders. When the A/F is above the stoichiometric value, there is significant excess oxygen for combustion and, consequently, an appreciable oxygen content in the exhaust. The zirconia-based oxygen sensor operates with ambient air at one electrode and the oxygen containing exhaust at the counter electrode. Under such A/F conditions, the voltage response of a zirconia-based oxygen sensor is fairly constant in the range of about 0.0 V to about 0.5 V. When the engine is momentarily operated at A/F below the stoichiometric value, the excess oxygen is immediately utilized in combustion of hydrocarbon fuel and much less oxygen remains in the exhaust. The voltage output of the sensor is typically increased to the range of about 0.5 V to 1.0 V at all A/F above the stoichiometric value.
The voltage response of the sensor changes abruptly from one such range to the other when the engine A/F changes from slightly above the stoichiometric value to slightly below, or vice versa. This change in voltage is subject to process variability, and the sensor output in the range 0.3 V to 0.6 V cannot be reliably used by a PCM for fuel control. This range corresponds to the approximate critical A/F range of the stoichiometric value ±1.0 A/F (i.e., 13.7 to 15.7 for gasoline fuel).
In accordance with this invention, it has been found that by continually introducing a suitable pattern of individual fuel injector biases of known size, at any given engine speed, high frequency A/F oscillations of desired amplitude are produced at the oxygen sensor location. The PCM controls the on time of some or all of the injectors to deliver amounts of fuel that deviate from the average amount prescribed by the current PCM determined fueling strategy. Such deviations are imposed in each engine fueling cycle in which it is desired to operate the engine in accordance with this invention. The imposition of these individual cylinder A/F imbalances, through fuel injector biasing, changes the on-off nonlinear characteristic of the O
2
sensor in the affected A/F range. The result is a modification of the steady state characteristic of the sensor so that a dependable proportional response of the O
2
sensor over an A/F range of, e.g., 14.7±0.5 is created.
For example, in a 4-cylinder engine, with the cylinder firing sequence
1
-
3
-
4
-
2
, running at a steady 1500 rpm, fuel injection events occur at 20 millisecond (ms) intervals or with a frequency of 50 Hz. On selected fuel injectors (2 or 4 injectors), the fuel pulse widths are altered to cause a slight perturbation of A/F. During such steady engine operation (e.g., at 60 kPa), a normal fuel injection period per cylinder of about 6.0 ms may provide near stoichiometric A/F. Instead, injection duty cycles of 6.6 ms, 6.0 ms, 5.4 ms and 6.0 ms in cylinders
1
,
3
,
4
, and
2
, respectively, are repeatedly introduced in the cylinder intake ports or directly into the cylinders.
These and like fuel imbalances, preferably introduced during each fueling cycle of engine operation, produce a fluctuation in exhaust oxygen content and, thus, in voltage output at each event. The imbalances, when introduced, will typically amount to about one to fifteen percent of the amount of fuel that the PCM determines to be injected in the next cylinder fueling event to maintain the desired A/F. Averaged values of these outputs provide a usable linear voltage response to changes in A/F. The magnitude of the imbalance in injection time, here, e.g., ±0.6 ms, produces a proportional range in the downstream oxygen sensor response characteristic around the stoichiometric A/F. Such alteration of the nature of the oxygen sensor characteristics over the selected A/F range is suitably utilized to achieve the desired A/F as follows.
In a family of substantially identical production engines, such as four-cylinder intake port

Affiliated with

Also associated with

Rating

Soft linear O2 sensor does not yet have a rating. At this time, there are no reviews or comments for this patent.

If you have personal experience with Soft linear O2 sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Soft linear O2 sensor will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFUS-PAI-O-2964701