Electrolysis: processes – compositions used therein – and methods – Electrolytic analysis or testing – For oxygen or oxygen containing compound
Reexamination Certificate
1999-08-25
2001-07-03
Warden, Sr., Robert J. (Department: 1744)
Electrolysis: processes, compositions used therein, and methods
Electrolytic analysis or testing
For oxygen or oxygen containing compound
C204S424000, C219S497000
Reexamination Certificate
active
06254765
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a method of regulating the temperature of a sensor for determining an oxygen concentration in gas mixtures, in particular in exhaust gases of internal combustion engines.
BACKGROUND INFORMATION
Sensors are used to preset a fuel-air mixture for operation of an internal combustion engine by determining the oxygen concentration in the exhaust gas of the engine. The fuel-air mixture may be in the rich range, i.e., the fuel is present in stoichiometric excess, so that only a small amount of oxygen is present in the exhaust gas in comparison with other partially unburned components. In the lean range, where more oxygen than air is present in the fuel-air mixture, the oxygen concentration in the exhaust gas is high accordingly.
Lambda probes are known for determining the oxygen concentration in the exhaust gas, detecting a lambda value>1 in the lean range or <1 in the rich range and lambda=1 in the stoichiometric range. In a known way, a Nernst measurement cell of the sensor supplies a detection voltage which is sent to a circuit arrangement. The detection voltage is determined here by a difference in oxygen concentration at an electrode exposed to the gas for measurement and at an electrode of the Nernst measurement cell exposed to a reference gas. The detection voltage increases or decreases according to the oxygen concentration in the exhaust gas. A solid electrolyte body which is conductive for oxygen ions is arranged between the electrodes of the Nernst measurement cell.
Such sensors must be heated to temperatures above approximately 300° C. in the active range in order to achieve the necessary ion conductivity of the solid electrolyte. To achieve an increase in measurement accuracy of the sensor, it is known that the operating temperature of the sensor can be controlled and regulated as necessary. It is known, in addition, that a heating device may be provided for the sensor and can be turned on or off in accordance with an operating temperature measured by the sensor.
To determine the operating temperature, it is known that an alternating voltage can be applied to the Nernst measurement cell and an a.c. resistance of the sensor can be determined with a measurement device.
A disadvantage of the known method is that the temperature-dependent a.c. resistance is determined by starting with a constant a.c. resistance of the electrodes, the solid electrolyte and the leads to the electrodes. The leads here have approximately 50% of the total resistance of the Nernst measurement cell in the operating state. Due to a manufacturing scattering, the lead resistance is subject to a relatively great scattering, so the measurement device determining the a.c. resistance of the Nernst measurement cell has an error corresponding to this scattering. The measurement device adds this scattering error to a temperature-induced fluctuation in the a.c. resistance and supplies a corresponding faulty control signal for the heating device of the sensor. This regulates the sensor at an incorrect operating temperature.
SUMMARY OF THE INVENTION
The method according to the present invention has the advantage that the operating temperature of the sensor can be regulated accurately. Due to the fact that an internal a.c. resistance of a lead of electrodes of the Nernst measurement cell is determined in starting or restarting operation of the sensor, and the instantaneous internal resistance of the lead thus determined is taken into account in determinating the operating temperature, manufacturing fluctuations in the resistance value can be eliminated. The internal a.c. resistance of the Nernst measurement cell then measured during operation of the sensor in fact fluctuates only because of a change in temperature, so that the control signal supplied by the measurement device for the heating device can be supplied with a great accuracy. In particular, it is also advantageous that a change in resistance due to aging can be taken into account in resuming operation of the sensor due to the repeated measurement of the internal resistance of the lead.
In another preferred embodiment of the present invention, the instantaneous internal a.c. resistance of the lead is determined by a brief overheating phase of the heating device, while the total internal a.c. resistance is being measured. A constant value for the resistance component of the electrodes and the resistance component of the solid electrolyte between the electrodes is subtracted from this measured internal a.c. resistance. This yields the exact internal resistance of the lead of the sensor. Furthermore, it is preferable if a temperature coefficient of the electrodes is taken into account in the determination of the instantaneous internal resistance of the lead, so that the accuracy in determination of the actual internal resistance of the lead can be increased.
The method according to the present invention also offers the advantage that overheating of the sensor is prevented. Due to the fact that an internal a.c. resistance of a lead of the electrodes of the Nernst measurement cell is determined during operation of the sensor, in particular during a shut-down phase of the sensor, and the instantaneous internal a.c. resistance thus determined is taken into account in determining the operating temperature, fluctuations in the internal a.c. resistance can be taken into account to advantage during operation of the sensor. This makes it possible to turn the heating device of the sensor off and on in a controlled manner, preventing overheating of the sensor which could lead to heat stress cracks in the sensor. In particular since the internal resistance of the solid electrolyte body of the Nernst measurement cell is very small at the operating temperature of the sensor, fluctuations in the lead resistance to the Nernst measurement cell have strong effects accordingly.
REFERENCES:
patent: 4419190 (1983-12-01), Dietz et al.
patent: 4505802 (1985-03-01), Mase et al.
patent: 5461902 (1995-10-01), Iwata
Kenyon & Kenyon
Olsen Kaj K.
Robert & Bosch GmbH
Warden, Sr. Robert J.
LandOfFree
Method of regulating the temperature of a 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 Method of regulating the temperature of a sensor, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of regulating the temperature of a sensor will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2507943