Measuring and testing – Gas analysis – Detector detail
Reexamination Certificate
1999-05-28
2002-09-10
Williams, Hezron (Department: 2856)
Measuring and testing
Gas analysis
Detector detail
C073S023320
Reexamination Certificate
active
06446488
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates generally to a gas concentration measuring device which may be employed in an air-fuel ratio control system for automotive vehicles to measure a given gas component contained in emissions from an internal combustion engine, more particularly to an improvement on a circuit structure of a gas concentration measuring device equipped with a gas sensor which, when applied with the voltage, produces an electric signal indicative of the concentration of gas.
2. Background Art
Recently, in order to meet requirements for improvement in control accuracy of automotive air-fuel ratio control systems and enhancement of lean burn of internal combustion engines, linear air-fuel ratio sensors designed to measure the concentration of oxygen contained in exhaust gasses of the internal combustion engine to determine the air-fuel ratio of mixture sucked into the engine linearly in a wide range and an air-fuel ratio measuring devices using the same have been proposed. As such air-fuel ratio sensors, a limiting current air-fuel ratio sensor as taught in, for example, U.S. Pat. No. 5,691,464 is known in the art which is responsive to application of voltage to produce a limiting current whose detectable range changes with a change in concentration of oxygen in exhaust gasses.
FIG. 1
shows an air-fuel ratio measuring circuit
80
employed in one example of conventional air-fuel ratio measuring devices.
The air-fuel ratio measuring circuit
80
includes a reference voltage generator
84
, amplifying circuits
85
and
86
, a current-detecting resistor
88
, and a voltage follower
89
.
The reference voltage-generator
84
produces a constant reference voltage Va. The reference voltage Va is amplified in current by an operational amplifier
85
a
of the amplifying circuit
85
. To one end of an air-fuel ratio sensor
81
, the voltage identical with the reference voltage Va is applied. An operational amplifier
86
a
of the amplifying circuit
86
amplifies in current a command voltage Vb produced from a D/A converter
87
. The voltage equal to the command voltage Vb is applied to the other end of the air-fuel ratio sensor
81
. The command voltage Vb is adjusted by a CPU (not shown) according to an instantaneous air-fuel (A/F) ratio.
The sensor current flows through the air-fuel ratio sensor
81
as a function of the A/F ratio of gases to be measured. A voltage drop across the resistor
88
caused by the flow of the sensor current, that is, a difference between the reference voltage Va and the voltage Vc is monitored by an external electronic control unit (ECU) to determine the value of the A/F ratio. The voltage Vc is inputted to the ECU through the voltage follower
89
. The value of the A/F ratio determined in the ECU is employed in the feedback control of the A/F ratio.
FIG. 2
shows a typical circuit structure of each of the operational amplifiers
85
a
and
86
a
. The operational amplifiers
85
a
and
86
a
have the same circuit structure, and explanation below will refer only to the operational amplifier
85
a
for the brevity of disclosure.
The operational amplifier
85
a
operates on a source voltage Vcc of 5 V. An input circuit
91
includes a pair of pnp transistors T
21
and T
22
which operate on the constant current I
1
from a constant current circuit C
1
in response to input signals IN+ and IN− to change the collector current as a function of a difference in voltage between the input signals IN+ and IN−. Changes in collector current of the transistors T
21
and T
22
will activate a pair of npn transistors T
23
and T
24
.
Specifically, when the input signal IN+ is higher in voltage than the input signal IN−, it will cause the collector current of the pnp transistor T
22
to increase, so that the collector voltage of the npn transistor T
24
is elevated. Alternatively, when the input signal IN+ is lower in voltage than the input signal IN−, it will cause the collector current of the pnp transistor T
21
to increase, so that the base current flows in the npn transistors T
23
and T
24
, thereby turning on the npn transistors T
23
and T
24
so that the collector voltage of the transistor T
24
drops.
The collector voltage of the npn transistor T
24
is transferred as a signal SG
1
to the intermediate amplifying circuit
92
. The signal SG
1
is amplified and outputted as a signal SG
2
to the bias circuit
93
. The bias circuit
93
operates on the constant current I
2
from the constant current circuit C
2
and activates the npn transistor T
25
working as a current source or the npn transistor T
26
working as a current sink.
When the input signal IN+ is higher in voltage than the input signal IN−, the bias circuit
93
activates the npn transistor T
25
to elevate an output voltage. Alternatively, when the input signal N+ is lower in voltage than the input signal IN−, the bias circuit
93
activates the npn transistor T
26
to decrease the output voltage.
Each of the operational amplifiers
85
a
and
86
a
, however, has the drawback in that a voltage output is produced only within a range narrower than a range from the source voltage Vcc to ground potential by given voltage losses. Increasing the accuracy in measuring the concentration of gas requires broadening the range of the output voltage.
The reason that the range of the output voltage is limited to be narrower than the range from the source voltage Vcc to ground potential will be discussed below.
The voltage of the input signal IN+ depends upon a voltage drop VI
1
across the constant current circuit C
1
and the base-emitter voltage VF
1
of the transistor T
21
(or the base-emitter voltage VF
2
of the transistor T
22
). Specifically, the voltage of the input signal IN− depends upon the voltage drop VI
1
and the base-emitter voltage VF
2
developed across the transistor T
22
. The transistors T
21
and T
22
, therefore operate normally within a voltage range below Vcc-VI
1
-VF
1
(or -VF
2
). If VF
1
=VF
2
=0.7 V and VI
1
=0.6 V, then a maximum voltage of each of the input signals IN+ and IN− is restricted to 5 V−0.6 V−0.7 V=3.7 V.
The npn transistor T
25
operates on the constant current I
2
from the constant current circuit C
2
and allow the base current to flow. An upper limit of the output voltage of the transistor T
25
, thus, depends upon the voltage drop VI
2
developed across the constant current circuit C
2
and the base-emitter voltage VF
5
developed across the transistor T
25
. Specifically, the upper limit of the output voltage of the transistor is limited to below Vcc−VI
2
−VF
5
. If VF
5
=0.7 V and VI
2
=0.6 V, then a maximum output voltage will be 5 V−0.6 V−0.7 V=3.7 V.
The pnp transistor T
26
is turned on, causing the base current to flow into the bias circuit
93
. If the base-emitter voltage VF
6
of the transistor T
26
is 0.7 V, then a lower limit of the output voltage of the transistor T
26
is restricted to VF
6
=0.7 V where a voltage drop of the bias circuit
93
is assumed to be zero (0).
Therefore, the voltage of output from each of the operational amplifiers
85
a
and
86
a
falls within a range of 0.7 to 3.7 V which is narrower than a source voltage-to-ground potential range of 0 to 5 V.
Additionally, when an air-fuel ratio of 25 is measured in a lean. burn range of the engine, the sensor current flowing through the A/F sensor
81
shows 22 mA. In this case, the base-emitter voltage VF
6
of the pnp transistor T
26
increases up to 1.2 V. The output voltage range of each of the operational amplifiers
85
a
and
86
a
will, thus, be decreased to 1.2 to 3.7 V. Note that if VF
6
=0.7 V as described above, then the sensor current=1 mA in a rich burn range of the engine.
SUMMARY OF THE INVENTION
It is therefore a principal object of the present invention to avoid the disadvantages of the prior art.
It is anot
Hada Satoshi
Kawase Tomoo
Kurokawa Eiichi
Suzuki Toshiyuki
Denso Corporation
Garber C D
Nixon & Vanderhye P.C.
Williams Hezron
LandOfFree
Gas concentration measuring apparatus producing current... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Gas concentration measuring apparatus producing current..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Gas concentration measuring apparatus producing current... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2870511