Measuring and testing – Volume or rate of flow – Thermal type
Reexamination Certificate
1998-11-10
2001-08-14
Patel, Harshad (Department: 2855)
Measuring and testing
Volume or rate of flow
Thermal type
Reexamination Certificate
active
06272918
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a thermal flow meter for detecting the flow rate of a fluid with a thermosenstive resistance, and more particularly to a thermal flow meter outputting a pulse-like signal corresponding to the flow rate of a fluid, and a fuel controller using the thermal flow meter adapted for, e.g., internal combustion engines.
2. Description of the Related Art
Generally, very high accuracy is required in flow rate conversion that is to be performed on a signal of a thermal flow meter in a fuel controller for, e.g., internal combustion engines. Therefore, a high-accuracy reference power supply is provided in the fuel controller, and A/D conversion is made on a flow rate signal on the basis of the reference power supply.
FIG. 9
is a block diagram showing an example in which a conventional thermal flow meter outputting a voltage signal is employed in a fuel controller for internal combustion engines.
In
FIG. 9
, a thermal flow meter
1
is connected to a fuel injection controller
2
which comprises a high-accuracy reference power supply
3
, an A/D converter
4
, and a microcomputer
5
. The thermal flow meter
1
includes an amplifier (not shown) which amplifies a flow rate signal applied thereto and outputs an amplified signal.
A voltage signal output from the thermal flow meter
1
is applied to the A/D converter
4
in the fuel injection controller
2
, and the applied voltage signal is A/D-converted on the basis of the high-accuracy reference power supply
3
. A resulting digital signal is used to carry out a process of fuel injection amount control in the microcomputer
5
.
FIG. 10
is a block diagram showing an example in which a conventional thermal flow meter outputting a current signal is employed in a fuel controller for internal combustion engines, the example being disclosed in, e.g., Japanese Unexamined Patent Publication No. 2-216420.
In
FIG. 10
, a high-accuracy reference resistance
6
is disposed between the input side of an A/D converter
4
and the ground side. The other structure is the same as shown in FIG.
9
.
In this example, a current signal output from a thermal flow meter
1
is subjected to current/voltage transformation (I/V transformation) by the high-accuracy reference resistance
6
in a fuel injection controller
2
, and then applied to the A/D converter
4
. The applied voltage signal is A/D-converted on the basis of a high-accuracy reference power supply
3
. A resulting digital signal is used to carry out a process of fuel injection amount control in a microcomputer
5
.
If a resistance value of the high-accuracy reference resistance
6
has a temperature characteristic or changes depending on the individuals, a resulting variation directly gives rise to an error of the flow rate. For this reason, the high-accuracy reference resistance
6
is usually formed of a resistor which is expensive and has very high accuracy.
In the conventional thermal flow meters, however, when it is used in combination with the fuel injection controller, the high-accuracy reference power supply is required for the A/D converter in the fuel injection controller to suppress an error that may occur during the A/D conversion. Also, in the thermal flow meter outputting a current signal, a high-accuracy reference resistance, which has a superior temperature characteristic or small variations (in temperature characteristic, resistance value, etc.) depending on the individuals, is required to suppress an error that may occur in the current/voltage transformation. There has been hence a problem that the conventional thermal flow meters are necessarily expensive.
SUMMARY OF THE INVENTION
With a view of solving the problem as set forth above, an object of the present invention is to provide a thermal flow meter which is relatively inexpensive and operates with high accuracy and reliability, and a fuel controller using the thermal flow meter adapted for internal combustion engines.
A thermal flow meter according to a first aspect of the present invention comprises a flow rate detecting unit for detecting a flow rate signal, a reference power supply for generating a reference signal, and switching means for selectively outputting the flow rate signal from the flow rate detecting unit and the reference signal from the reference power supply. With the first aspect of the present invention, the flow rate signal and the reference signal can be transmitted by one signal line. Therefore, highly accurate signals can be transmitted without being affected by resistance components of the line and an interface, etc. Further, the number of transmission lines can be reduced.
A thermal flow meter according to a second aspect of the present invention further comprises timing signal generating means, in addition to the first aspect, wherein the switching means selectively outputs the flow rate signal and the reference signal in response to a timing signal from the timing signal generating means. With the second aspect of the present invention, the need of inputting the timing signal from the outside is eliminated and the number of transmission lines can be reduced.
A thermal flow meter according to a third aspect of the present invention further comprises, in addition to the first aspect, amplifying means for amplifying the flow rate signal and the reference signal and then outputting the amplified signals as voltage signals. With the third aspect of the present invention, the flow rate can be measured without being affected by the accuracy of the amplifying means.
A thermal flow meter according to a fourth aspect of the present invention further comprises, in addition to the first aspect, amplifying means for amplifying the flow rate signal and the reference signal and then outputting the amplified signals as current signals. With the fourth aspect of the present invention, the effect of a difference in GND potential between the thermal flow meter and a fuel controller, for example, connected to the thermal flow meter can be eliminated.
In a thermal flow meter according to a fifth aspect of the present invention, in addition to the first aspect, plural items of information are output via a single transmission line by using plural factors selected from among a frequency, duty and voltage level which are contained in the flow rate signal. With the fifth aspect of the present invention, the number of transmission lines can be reduced.
A fuel controller according to a sixth aspect of the present invention is made up of a thermal flow meter comprising a flow rate detecting unit for detecting a flow rate signal, a reference power supply for generating a reference signal, and switching means for selectively outputting the flow rate signal from the flow rate detecting unit and the reference signal from the reference power supply, and signal processing means for calculating a flow rate of fuel based on the flow rate signal and the reference signal from the thermal flow meter. With the sixth aspect of the present invention, the flow rate of fuel can be controlled without being affected by the accuracy of a current detecting resistance in a fuel control system.
In a fuel controller according to a seventh aspect of the present invention, in addition to the sixth aspect, the signal processing means discriminates an input signal from the thermal flow meter and handles the input signal as the reference signal when the input signal is outside a range of the flow rate signal. With the seventh aspect of the present invention, the flow meter signal and the reference signal can be easily discriminated from each other.
A fuel controller according to an eighth aspect of the present invention, in addition to the sixth aspect, the signal processing means determines the thermal flow meter to be failed when the input signal from the thermal flow meter exceeds a predetermined value and continues for a predetermined time. With the eighth aspect of the present invention, since a time factor is essentially added as one of the conditions for failure
Mitsubishi Denki & Kabushiki Kaisha
Patel Harshad
Sughrue Mion Zinn Macpeak & Seas, PLLC
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